BOOK I. 



GENERAL MORPHOLOGY. 



CHAPTER L 



MORPHOLOGY OF THE CELL. 



Sect. i. Preliminary Inquiry into the Nature of the Cell. — The sub- 

 stance of plants is not homogeneous, but is composed of small structures, generally 

 indistinguishable by the naked eye. Each of these is, at least for a time, a whole 

 complete in itself, being composed of solid, semi-solid, and fluid parts which differ 

 in their chemical nature. These structures are termed Cells. For the most part, 

 large numbers of them are in close contact and firmly united; and they then 

 form a Cellular Tissue. But in every plant which completes its term of life there 

 is at least one period in which certain cells or groups of cells separate at definite 

 points from the union, and, after isolation, begin for themselves an independent 

 course of life, as spores, pollen-grains, oospores, gemmae, &c. 



Like the shape and size of the whole plant, the form, structure, and size of 

 its individual cells are subject to regular changes ; and the nature of these cannot be 

 ascertained from the study of a single phase, but only from the entire series of 

 changes which may be called the life-history of the cell. And as, moreover, each 

 cell fulfils its own definite part in the economy of the plant, i. e. is specially intended 

 for certain chemical or mechanical purposes, so also cells exhibit a diversity of 

 form corresponding to their different functions. These differences, however, do 

 not usually arise until the cells have passed through their earlier stages; the 

 youngest cells of a plant differ only slightly from one another. 



The general morphological laws which prevail in all cells are also more clearly 

 evident in the young state ; the more the developing cells adapt themselves to the 

 special purposes which they have to fulfil, the more difficult it becomes to recognise 

 in them these laws, which we will now expound more in detail. 



By far the largest proportion of cells in the living succulent parts of plants, 

 such as young roots, leaves, internodes, and fruits, are made up of three con- 

 centrically-disposed parts. First is an outer skin, firm and elastic, the Cell-wall, 



B 



