ELEMENTARY STEUCTUEE. 13 



CHAPTER 2. 



ELEMENTARY STRUCTURE OF PLANTS, OR TEGETABLE 

 HISTOLOGY. 



Section 1. Of the Cell as an In-ditidual. 



The description of the elementary structure of plants is termed 

 Vegetable Histology. 



All plants in their earliest condition are composed of one {figs. 

 1-3), or more {figs. 4-6), delicate membranous closed sacs, called 

 cells or utricles. All the organs which afterwards make their 

 appearance in the plant are also made up of these little bodies, 

 variously modified according to circxmistances. The simple cell 

 presents itself, therefore, as the first and most important organ 

 of the plant — that from which all the others are developed ; and, 

 consequently, the only real elementary organ possessed by it. 

 It demands therefore our particular investigation. In treating 

 of it, we shall first describe its form and size ; then jirocecd to 

 investigate the nature of the membrane of which it is composed ; 

 and lastly, its contents. 



1. JFoRM OF THE Cell. — The cell in its earliest condition con- 

 sists of an exceedin gly thin struct ureless membrane , enclosing 

 various substances, wnen developed in a space where it is per- 

 fectly free from the pressure of surrounding bodies, and when 

 equally nourished at all parts of its surface, it assumes a more 

 or less rounded form {fig. 17) ; t he sphere is,, therefore, to be con - 

 sidered as the typical form of aT cell. This tendency, however, 

 of cells to assume a spherical form must be received with some 

 limitation, it being distinctly understood that such will be the 

 case only when they are developed under the above conditions. 

 But in the great majority of cases, as cells are formed by the 

 division of older cells (as will be hereafter seen), it must neces- 

 sarily happen, that when first developed they will have the 

 shape of the half, the quarter, or some other section of the parent 

 cell, according to the number of parts into which it may be 

 divided. Such cells, however, if unrestricted in their after 

 development, will then tend in the majority of cases to assume 

 a spherical form. But, in consequence of cells being usually 

 developed in a confined space, a number of other forms are pro- 

 duced, all of which depend upon two circumstances. In the first 



corresponding irregular growth 



