FORM OF THE PLANT-CELL. 39 



sequent irregular distension. Several forms of this nutrition may 

 be distinguished. 



A. Many-sided) or a nearly uniform) nutrition. From this arises 

 globular or elliptic cells ; or, if pressed on all sides, polyedral cells ; 

 or, in a regular arrangement, dodecaedral cells. When the parts 

 deposited are unconformable, little protuberances projecting on all 

 sides in the form of rays are developed, which constitute stellate 

 cells. 



B. Nutrition in the dimensions of the plane. From this arises 

 tabular cells; or, if the nutrition goes on in three dimensions of one 

 side, plano-convex cells ; but if the nutrition goes on in one direction 

 of the surface, then long small tabular cells, which may be called 

 strap-shaped. With an irregular extension this form of nutrition 

 developes rayed or stellate cells. 



C. Nutrition in one direction, extension in length only. The cells 

 formed are the cylindrical, prismatic, and fibrilliform. 



That an irregular nutrition is the principal cause of the variety in the 

 forms of cells is in the highest degree probable. Cells which are not 

 immediately in contact can only be nourished in those spots where they 

 are in contact with other cells ; and cell-walls in contact with air do not 

 continue to grow in that direction, but become flattened, as in the upper 

 surface of epidermis cells, and in the cells of the partition-walls of air- 

 passages on both sides. In the air-passages, when young, there are 

 globular cells which touch only at particular points : from the rapidity 

 with which the sap passes through these spaces, and is decomposed by 

 the air, these cells are only nourished at the points where they touch, 

 and the points of contact continue to grow, so as to form rays which 

 constitute the stellate cells of the partition walls, and the spongiform 

 cells of the air- passages. This irregular nutrition may also take place 

 in cells with perfect contact : in these cases the projecting rays are dis- 

 posed alternately, as is the case in many epidermis cells, whose edges 

 appear waved or toothed on the surface. 



But the most decided proof that irregular nutrition of the cell-wall is 

 the cause of the various forms of cells, has been afforded by Nageli*, in 

 his researches upon Caulerpa prolifera. It consists of a little creeping 

 stem with roots below and leaves above, and sometimes forming branches 

 on the sides, and originates in the growth of a body which may be 

 regarded as an individual cell. The large size of the parts admit of an 

 easy distinction being made between the old and young cells, as well as 

 the origin of the various forms from the differing nutrition of the 

 individual parts of the cell. The diversity of growth in individual cells 

 admits of analogy between the morphological distinction of stem and leaf 

 in the higher plants, as between the leaf and stem divisions of the single 

 cell in the present case. 



All the various forms of cells, with the exception of the globular, 

 elliptic, and fibrilliform, originate in the combination of many cells with 

 one another. Every free cell forms for itself an arched surface ;. polye- 

 dral cells originate from the mutual pressure of cells. If perfectly 

 formed cells of the same size are allowed to press against each other, they 

 will form rhombododecaedrons. The rhombododecacdron, although fre- 

 quently present, must not be regarded as the primitive form of the cell. 



* Schleiden and Nagirli, Zcitschrift fiir wissentschafUicho Botanik, part i. p 1 34 1 G5. 



D 4 



