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.