78 



LECTURE VI. 



presents itself as a slimy, or occasionally gelatinous, or sometimes more or less 

 solid mass; and either completely fills the cavity of the cell, or only clothes the , 

 wall as a thin layer, or traverses the "sap cavity of the cell in the form of a 

 network. 



This is the universally known and yet essentially unknown protoplasm, that 

 substance which, according to the researches of the last forty years, represents 

 the proper living body of every cell ; and which, as has been gradually proved, 



is the actual basis of life of 

 all organisms, both of animals 

 and of plants, and the investiga- 

 tion of which therefore, in our 

 time especially, is the object 

 of the Zoologist and Botanist. 

 In the protoplasm itself, again, 

 is found the nucleus of the 

 cell, which generally pre- 

 sents itself as a definitely 

 formed part of the protoplasm. 

 Only one nucleus is usually 

 present ; but in large, and espe- 

 cially in elongated cells, several 

 or many nuclei may be distri- 

 buted in the protoplasm. More- 

 over, particularly in the non- 

 cellular plants among the Algae 

 and Fungi, hundreds, or even 

 thousands of nuclei may be 

 found in the protoplasm, where 

 formerly, up to the year 1878, 

 their presence had been alto- 

 gether overlooked. 



From what has been stated, 

 the protoplasm, with its nu- 

 cleus, and the cell-membrane 

 or cell-wall, appear as the 

 essentials of every vegetable 

 cell. The other visible sub- 

 stances are temporary struc- 

 tures, nutritive materials, pro- 

 ducts of metabolism, or refuse matters and the like, to which we shall return in 

 detail when we are considering the theory of nutrition. 



For the present, however, we will keep to the . essential ■ constituents of the 

 vegetable cell— the protoplasm, nucleus, and membrane ; and these we will now 

 study more in detail. 



The Protoplasm, the fundamental significance of which for the whole life of 

 the plant has been already indicated, consists of albuminous substances, i.e. of 



Fig. 75.— Parenchyma cells from the middle layer of the root-cortex of 

 Fritillayia itnperialis (longitudinal section X 550). A very young cells still de- 

 void of cell-sap, lying close to the apex of the root ; B cells of the same descrip- 

 tion about 2 mm. from the apex of the root ; the cell-sap (j) forms isolated drops 

 in the protoplasm (p) ; plates of protoplasm separate these drops. C cells of the 

 same description about 7—8 m. m. from the apex of the root ; the two cells to the 

 right below are seen from the front, the large cell to the left below is in optical 

 section. The cell to the right above is opened by the section ; the cell-nucleus 

 shows a peculiar appearance of swelling under the influence of the penetrating 

 water \x y). 



