68 PART II. ANATOMY AND HISTOLOGY. [ 22 



millimeter in diameter), others obtain a considerable size (from 

 0-1 to 0-5 millim.), so as to be distinguishable even by the naked 

 eye (e.g. in pith of Dahlia, Impatiens, Sambucus). Many grow 

 to a length of several centimetres, as the hairs upon the seed of 

 Gossypium (cotton) ; and if coenocytes be included, such as the 

 laticiferous tubes of the Euphorbiacese, the Siphonaceous Algse, 

 and the Phycomycetous Fungi, very much larger dimensions in 

 length are attained. 



The Form of such cells as constitute an entire individual, or 

 exist independently, not forming part of a tissue (e.g. spores), is 

 generally spherical, or ovoid, or cylindrical. The different organs 

 of highly organised plants consist of many varieties of cells, and 

 even in the same organ cells lie side by side which are of very 

 different form. The two main types of cells are, first, such as are 

 spheroidal or polyhedral, with nearly equal or slightly differing 

 diameters (Fig. 36), as in pith, juicy fruits, fleshy tubers; and 

 secondly, such as are narrow and greatly elongated (Fig. 72), as in 

 the case of fibres. 



22. The Protoplasm. The protoplasmic contents of a cell 

 present certain clearly differentiated portions. In the first place 

 there is a nucleus ; and there are more or less numerous plastids. 

 These all lie in the general protoplasm of the cell which may be 

 distinguished as the cytoplasm. 



a. The Cytoplasm is of viscid tenacious consistence, but it is not 

 a fluid. Chemical examination shows that it consists (at least, 

 when dead) of proteid substance ; intimately 

 associated with this are varying quantities 

 of other organic substances, such as fats, 

 and carbohydrates, together with water, 

 and a small proportion of inorganic ash- 

 constituents. As it is the seat of all the 

 nutritive processes of the cell, it must ob- 

 viously contain at different times all the 

 various chemical substances which enter 



FIG. 37. Resting nucleus 

 from the young endosperm lnto > or are formed within the Cell. 



of F,;iairia imperial*. b. The Nucleus is always situated in the 



bowing the flbrillar net- i =rr * 



work with iu chromatin- cytop^sm. It consists of various proteid 

 granules, and several i. u - substances. Its structure, when at rest, 

 xTl)!^ y ^ generally described as follows. It 



is bounded at the surface by a membrane 

 which belongs, however, to the cytoplasm. It consists mainly of 



