The Morphologist

WHILE The Morphologist agreements mostly with the external pattern of the body components of the plant's body, the anatomist inquires into the interior structure of those identical body components, and investigates the placement of the tissues of which they are composed.

The vegetation body, like that of the animal, is constructed up of several distinct tissues, each of which has its function to present in the finances of the whole organism. In the animals there are skeletal components, muscles, nerve fibres, fat, and so on ; in plants there are wood, ground tissue or parenchyma, reinforcing tissue or sclerenchyma, and so on. The physiological functions performed by each of these groups of tissues is usually the same all through the entire animal and vegetation kingdom. Thus the skeletal components, for demonstration, anything their form or arrangement, pattern the support of the body, and to them the sinews are adhered ; the nerves, whatever their design of circulation, are the passages through which stimuli and tense notes are passed. In plants, anything its structure, the timber assists as the channel for the conduction of water ; and the sclerenchyma, wherever it may be put, is there for the purpose of reinforcing or defending the body part in which it develops. Hence, though it is neither shrewd neither possible to end wedding ceremony solely the study of anatomy from that of physiology, the major work of the anatomist agreements with the tissues themselves, and anxieties itself with their individual individual characteristics and the relative study of their development in the distinct instructions of organisms.

The vegetation body is created of jive primary kinds of tissue. These are the Epidermis, or skin, with its hairs and other secondary expansion ; the Parenchyma, forming the general ground tissue of the vegetation, with a number of secondary modifications ; the Sclerenchyma, or thick-walled reinforcing tissue ; and the vascular tissue, which is of two types, viz., the Wood, which is thick-walled, and conducts water and furthermore assists to strengthen the vegetation, and the Bast or Phloem, which forms the conduit for the route of the elaborated food-stuffs. For the higher plants, whereas there is much exact kind, there is a attribute design for the placement of these tissues in each of the organs root, arise, and leaf.

In origins there is no factual epidermis, but the outside cells of the juvenile origin are expanded to pattern long hairs with thin absorbent walls. The parenchymatous ground tissue types the major mass of the origin, and the vascular tissue is a compact, centered strand. In most roots there is no pith, and the timber types a solid mass in the centre with assemblies of the phloem out-of-doors it. This cylinder is closed off from the surrounding ground tissue by a focused sheath, which is usually much better developed in origins and in the smaller plants, such aa ferns and lycopods, than it is in the other body components of the higher plants, though it is occasionally apparently marked in their stems.

Stems have an epidermis while they are juvenile, and this shielding level is restored by an ever increasing secondary outer garment of cork as they boost in size. The ground tissue parenchyma may be changed into several kinds of units fcr distinct reasons, and in juvenile stems, which are green, the outside levels of the parenchyma usually comprise minute green kernels, the chlorophyll granules which play such an significant part in the manufacturing of food. Often blended with the parenchyma, in normal strands 'or assemblies, are thick-walled sclerenchyma cells, and their place in the arise is almost always that which is mechanically most advantageous.

In arises there is usually a pith of supple parenchyma cells, and around that the vascular tissues are arranged in assemblies, each assembly created of a strand of wood and a strand of bast. As the arise develops these separate strands of vascular tissue are connected to pattern a ring by secondary formations of timber and bast. Instead, therefore, of the centered, solid strand of Vascular tissue, as in the origin, the arise is distinuished by a hollow cylinder which is formed around a centered pith. In some few arises of the higher plants, out-of-doors this cylinder an endodermis sheath like that in the origin can be glimpsed, and this is a detail which is of much theoretical importance.

There are numerous outlooks as to the genuine significance and origin of the woody cylinder, and the one which seems to be best sustained by details considers the hollow vascular cylinder to be the descendant of a solid strand not different that in the origin, the centered units of which lost their feature as timber units and became simple parenchyma. The arises, which are maintained for us as fossils, appear to support this outlook, though at first sight it may sound rather far-fetched to state that the cells of the parenchyma on one edge of the vascular strands have a distinct worth from those on the other side of the identical strands.

Probably one of the most mighty leverages in the development of the timber on these lines was the mechanical advantage which was thereby profited, for, with the same number of thick-walled timber units, a stronger column is made when it is in the pattern of a cylinder than when it is solid. The timber units in the arise have not only to perform the water present to the leaves, FIG. 3. Transverse part of part of a arise of Aristolochia, displaying the different types of ground tissue and vascular cells. The four biggest cells in the centre are timber vessels, and the slender level of units just behind them, is the cambium level which devotes increase to the new tissue year by year. but have furthermore to play a large part in producing the stem strong sufficient to stand upright. As the arise gets older the ring of lesser wood and bast rises substantially, and in perennial plants solid rings of timber are supplemented year by year which shortly dwarf the initial prime assemblies of timber, and they cease to function after a time. In trees and woody shrubs the formation of the lesser zones of timber increases largely, and they become the primary characteristic in the trunk. The formation of rings of lesser timber takes place furthermore in origins, in order that when they are very old, and the inward tissues are trampled, it is not so straightforward to disguish them from stems. The prime organisations, although, are effortlessly distinguished, and when there is any question from the external morphology solely as to if any body part is a root or a arise, a part displaying the interior tissues will set up its nature.

The leaf, with its flat amplified exterior, disagrees from the arise and origin in having a bilateral and not a radial symmetry. In a usual dicotyledonous leaf the single vascular strand which sprints out from the arise into its petiole parts in one plane to pattern a entire network like a fan. Each finer agency of the vascular strand in this is like the one from which it originated, and is created of a lone assembly of timber units and a group of bast units edge by side. Between the meshes of this fan, webbing the entire simultaneously, is the soft-celled parenchyma. In most situations the top levels are more closely crammed and created of more normal cells than those on the smaller edge, and usually all of them contain many green granules of chlorophyll. Enclosing and defending this world broad web of tissue on both sides is an epidermis. In numerous situations, especially in the tough departs of plants which augment in hard conditions, there are reinforcing musicians and props of sclerenchymatous tissue organised to large mechanical advantage. To the theoretically minded anatomist, and him who concerns himself with the phylogeny of vegetation structures, the utmost concern lies in the woody tissue. Not only is this simpler to identify and stain in dwelling plants, but it is better maintained in the fossils than the suppler cells, and has more feature ; while the other tissues seem to assembly themselves around it. It is to the plant's body what the bony skeleton and the arterial system combined are to the animal. It is therefore not surprising that most work on vegetation anatomy delicacies principally of the woody cylinder.

What we have advised so far has been the vascular arrangement in the largest and most significant family of plants, the blossoming plants. In the smaller families, both dwelling and extinct, there are numerous other types of arrangement. The study of anatomy, therefore, bears on methodical botany, for the unchanging internal characters of the body components pattern dependable criteria for the separation of the distinct groups. The spectacular characteristics in the anatomy of the other principal assemblies of plants is as pursues : The Gymnosperms (the pine-tree group) have a general structure alike to that of the Dicotyledons. Their wood disagrees, although, in the feature of its uniform cells and in the pitting of their partitions a issue we have not yet considered. They have a depression primary cylinder with lesser zones of timber, rather similar to those in the blossoming plants.

The Ferns, as they are now comprised by the living species, are very distinct in their arise anatomy from these higher plants. In the first location, the primary organisation of their arises displays large variety in type in the distinct species. Yet the most agree in having several distinct strands, each organised like that of the origin of the higher plants in so far as it has the timber in the centre with the bast surrounding it, and that each such strand is closed off from the surrounding parenchyma by a particularly coordinated sheath the epidermis. In a couple of ferns a lone depression cylinder is organised on this design, but in most there are several strands, and in numerous ferns the number of anastomosing strands is very large. In no one of the dwelling ferns are these prime strands joined by any secondary growth of woody tissue. In the Lycopods the arrangement, though with one-by-one peculiarities, is much like that in the ferns. So long as only dwelling types were studied, it was considered that the formation of secondary wood was a feature only evolved in the Gymnosperms and the blossoming plants. Since the anatomy of the fossils has been revised, although, the remarkable fact has arrive to lightweight that in the early and extinct forms of the ferns and the Lycopods, and even of the Equisetaceae, lesser woody tissue was developed in substantial amounts, and evidently on the same plan as is now discovered in the Gymnosperms. Their primary organisations were like those of their dwelling representatives, and rather different the higher plants. It is nearly unanimously factual that the prime structures of the vegetation are the truest tour guides to its affinity. The development in time past of the lesser timber in the Lycopods and other extinct Pteridophytes was at a time when they were amidst the biggest tree-like forms of plants then extant. To support their strong shafts and to provide their crest of departs with water it was necessary to have added woody tissue, which was developed in the most clear-cut and simplest way in radial rows of cells. That Lycopods to-day manage not develop such timber is doubtless due to the detail that they manage not grow to such a dimensions as to need it. But, when we ask why we manage not now find them increasing to such a size, we have left the province of anatomy and went into the philosophical area in which doubt still reigns. In the families underneath the ferns there is little that greatly concerns the vascular anatomist. The Mosses have but little differentiation into factual tissues, though the wellknown genus, Polytrichum, has certain thing corresponding to timber and phloem cells.

The Algae have no differentiation into factual tissues, and only some of the biggest of them, the Laminarias, show any thing close to the vascular units of the vascular plants. In them there are zones of elongated cells with sieve-like plates between which distinctly resemble some of the bast units in higher plants. The thread-like algae and the fungi are easily composed of somewhat differentiated units which are fundamentally parenchymatous. For anatomical concern, then, we must come back to the Pteridophytes and the higher plants. From a study of the present-day ferns and the many fossil genera of Pteridophytes and that extinct group, the Pteridospermae, it seems that a large numerous varieties of placement of the woody tissues have been attempted by plants. Many of these were much more convoluted than the straightforward depression cylinder which is now discovered in the most thriving and largest types. It seems almost as though the present straightforward kind of structure were the outcome of decrease from certain thing more cumbersome. The remnant of the endodermis, for example, which is discovered in some Dicotyledon arises to-day, is one of the signs that propose this. Further, while it is out of the inquiry in the present state of our knowledge to load up in the breaches in a direct sequence of descent, it is yet likely amidst the fossils of distinct families to display a conceivably aligned sequence in which the simple hollow cylinder of timber is attached with foims which had a solid centered mass of timber, and, afresh, with others in which the pith was starting to be formed in the middle of it. In the anatomy of all plants the relative of the leaf strands to the vascular tissue of the main arise is a very significant factor. In the modern higher plants the prime vascular strand transient up the arise passes exactly out to the leaf stalk, so that the leaf strands and those from the arise are the same and pattern one system. In some of the smaller plants, and in numerous of the fossils, this does no emerge to be so, and it is likely that in the early types the stem had a scheme of vascular strands of its own which helped to perplex affairs for those who theorise.

Morphology Exemplar

The hard  dark   levels  which  enclose  and  defend  the delicate foliage departs in the bud are themselves simply leaves which have been changed for this purpose. In some buds, for demonstration the Horse Chestnut, you can A spiny cactus, displaying the circular fleshy arise which is green, and performs the nourishment assimilation rather than of the leaves. The factual departs are modified into hard spines.

Find a stepwise transition from the outermost dark hard scales to the inward ones, which are supple and green. In some plants the departs are all changed and hard, and the arise does the work of assimilating. For example, in the Cactus the departs are all decreased to needle-like spines, but the arise is supple and fleshy and reen- tinted, and manufactures all the food. The rounded fleshy mass of the arise reveals much less surface for evaporation than would the laminae of ordinary departs, and the vegetation is therefore adept to inhabit very arid regions.

A large compare to the Cactus, with its pudding-like stem, is the dainty Creeper that is not powerful enough to stand alone. Here the departs, rather than of being reduced, have added work to manage, for when a plant economises in the tissue it places into its arise, and has a slim axis needing support, it may call on its leaves to aid it in adhering itself. The Sweet-pea does this, and at the finishes of its aggregate departs some of the leaflets are decreased and changed into tendrils, which are perceptive and motile and cling to any support.

The well-known creeper, the Ampelopsis, is another example of this, in which case the entire of one leaf in each two is changed to pattern some tendrils, each ending in an adhesive disc. One of the strangest modifications of departs is that in attachment with the arrest of bug prey. The Sundew (Drosera) with its red departs enclosed with sparkling tentacles, the sickly yellow departs of the Pinguicula, and the odd and complicated Pitcher plants of all kinds have changed and elaborated their leaves to make tricks for the bugs they capture and use as food.

Though the departs routinely are sustained by the stem, there are not liking situations where the leaves have become the support of the entire vegetation, as, for instance, the large Stag's-horn fern, which is adhered to tree trunks, and, with its large shield-like departs, forms a bracket which catches fragments of dirt and holds the water, forming a kind of flower-pot in which the roots ramify. Even more specialised "flower-pots" are renowned in the tropical, rock-inhabiting Discidia. In this vegetation one leaf of a two types a bag, much like that of a Pitcher vegetation, in which the adventitious origins from each node are contained.

Such farthest modifications are odd, but every normal vegetation has diverse types of departs, and we must now turn to the changed departs which join to form, with all their infinite diversity, what we call the flower. The absolutely crucial components of the bloom are the sexy cells, but, like the one-by-one tissue units, these are very minute, and so, for their defence and aid, a number of departs have become especially changed on a given plan which, in its fundamental elements, is widespread to most flowers.

The outside departs of a bloom are shielding, and these are usually green or dark and of powerful texture. In most of the higher plants they have a decisive number, often three, four, or five. Within them the next set of departs is usually more glaringly tinted and of more dainty texture. To this exceptional sequence of leaves the title corolla is granted, and the one-by-one leaves are called the petals. Their work is solely different from that of commonplace departs, and, while it is partly  protective, their use is mostly to make the flower attractive to the bugs which arrive (or .used to come in the past) to convey the pollen which consequences cross pollination. We next arrive to the more important "leaves," which are decreased in general to little stalks, bearing the male sporangia, called the pollen sacs. The Sporangia pertains to a distinct class of body part, and though they originate on the changed (and in some families on the normal) departs, they are distinct from them in just the identical sense that the leaf is distinct from the stem that bears it. Indeed the distinction is more fundamental when one proceeds back to the source of things, for the simplest types of plants have only two kinds of units, the vegetative and the sporangiate.

These decreased departs of the bloom and their spore sacs are called stamens ; the pollen kernels, or spores which they make, comprise the male nuclei. The reduced stalk-like "leaves" of the stamens have a great inclination in numerous blossoms to enlarge and become petal-like. The large blossoms of the Rhododendron commonly display numerous intermediate phases between ordinary petal departs, through half decreased petals with one or more anthers, to the usual stamens. The "doubling'' of Buttercups, Cherries, and such flowers is due to the larger part or all of the stamens becoming petaloid. When the increasing two-fold is entire the flower cannot make any pollen of its own, and should either be pollinated from the lone blossoms or stay sterile. We have voiced of the output of the male nuclei in the pollen, and this, of course, presupposes the existence of a feminine cell with which it can fuse. These female units are made in "ovules," which are contained in one or more situations or carpels lying in the centre of the flower. These organisations are exceedingly complex, and the minutia of their morphology need much study, and are still the subject of enquiry and discussion.

There is, although, no question that the shut cases or carpels which comprise the ovules comprise a leaf in which the borders have revolved over and connected up to  form a little bag-like structure. This may be entirely  closed, or may are inclined subsequent to divide open afresh, as it does in the Larkspur, for demonstration, when the kernels are ripe.  The unfertilised kernels or ovules encompassing the eggcell develop on the inward borders of the carpel leaves, and are therefore defended by the shut bag they form. In numerous minutia the ovules correspond to sporangia, but they are not easily sporangia, and they have added to them some outer garments and inward tissues which no simple sporangium has. The egg-cell, although, is the fundamentally important characteristic in them, and it is with this cell that the male nucleus fuses, and it is for the sake of conveying these two units simultaneously, and defending the young embryo formed after their fusion, that all the complexity of the bloom has been developed. How complex it is, and how very vintage its annals, one can only  realise after revising the fossil kinds which have gradually led up to it.

Some of the fossil kernels from the Coal Measure period are even more convoluted than those of the present day. We have now observed soon all the body components of a plant. It is probable that a book reader will directly believe of fruits and kernels which emerge such distinctly characteristic structures. They are, although, but modifications of the components we have currently mentioned. The kernels are but the ovules enlarged with the increasing embryos, in their tissues storehouses of nourishment, and with the outer ovular outer garments hardened. The crop, if fleshy, winged, or plumed, is a farther development and modification of the carpel departs or of some carpel leaves fused simultaneously, or of the carpels with some of the other flower-parts adhering to it and ripening with it, instead of being lost when the blossoming was done. The only new thing in the fruits and kernels is the embryo, and that starts a new cycle and pertains to a new generation. It is created, although, of the fundamental vegetative body components a origin, a arise, and the first leaves. These body components are made in miniature in the kernel, and then they lie there for a long resting period in most plants.

The germination of the kernel is the rousing of these same body components to life and farther growth. In the growth and development which pursues the germination of the seedling there are numerous characteristics of substantial morphological interest. The juvenile vegetation often tends to repeat in its own life annals some of the phases through which its species passed as a entire in its evolution. Thus we find in the development of plants with divided, complex departs that the first three or four departs of the seedling are easier, and it is only as it develops that it attains the complicated mature individual foliage. Plants, too, which have focused arises or complicated organisations to replace ordinary foliage, will usually have a much simpler and more usual structure when they are very young. The study of seedlings is, thus, a very useful component in trying to elucidate some of the morphological problems. So far we have advised only the body of the higher plants, in which, though there is infinite kind of detail, there is a uniformity of design throughout. Among many of the smaller plants we find the vegetative body composed of the identical set of body components origin, arise, and leaf as in the case of the higher plants. Further comparison is rendered more tough by the detail that the alternation of generations, widespread to almost all plants, is in them conveyed in periods of two distinct individuals, and a little green vegetation (known as the Prothallus) bears the sexy units of the large, leafy fern. The prothallial vegetation is made from the spores of a simple kind which are often conveyed, not on blossoms, but on the ordinary foliage of the vegetative plant. All our common ferns have this feature, and the brown marks on the departs are clusters of little sporangia, while the little prothallial vegetation they make is usually solely neglected and unseen be obliged to its minute size. The mosses furthermore have an alternation of generations, but in their case the turn around is factual, and what we understand as the moss vegetation is the prothallial generation, which has elaborated itself in order that it has much the look of a leafy vegetation, though it is so different in its source from the leafy plants of other groups.

In the algae we find the vegetation body comprised by easier structures. The entire algal body is often called a thallus, and this has districts which correspond more or less nearly to origin, arise, and departs in the more complicated and bigger of the seaweeds. In most algae, although, there is little differentiation amidst the units, and in the straightforward hair-like types so widespread in the new water ponds and creeks, there are only green vegetative units and reproductive units with no modification into factual "organs." In the fungi we get furthermore a very straightforward vegetation body, usually like that of the thread-like algae. Sometimes numerous of these filamentous units intertwine to pattern rather large and evidently convoluted bodies, the toadstools for example, but the plants have not really differentiated organs.  It is intriguing to observe how several the higher plants have degenerated and lost the differentiation of their parts. For demonstration, the Dodder (Cuscuta), which develops with such dangerous achievement on the Clover and Furze, seems to have lost all differentiation of arise, origin, and departs, and has become a meagre tangle of fine pinkish fibres, which adhere themselves to the arises of other plants and draw all nourishment from them. Its blossoming, although, it should manage for itself, and the components of its blossoms, which emerge in somewhat large clusters on the slim arises, are rather normal. One  of the most intriguing situations of a decreased structure is the vegetation body of the giant-flowered Rafflesia. This has the biggest bloom in the world, and it seems to have no vegetative body at all ! That is because it is so absolutely parasitic that it gets the entire of its nourishment from a owner on which it preys, in order that it can pay for to decrease its own vegetative body to the smallest, viz., a sequence of white fungus-like gist which are surrounded in the body of the host. In this vegetation origins, arises, and departs are all gone except for the changed departs of the flower.