44 BIOLOGY. [BOOK i. 



two small spherical or ovoidal bodies, likewise azotised. These 

 are the nuclei, in which are often included one or two nucleoles. 

 These azotised portions of the cell appear to be the seat of a 

 nutritive movement more intense than the others. They appear 

 also to be bound up with the period of development ; for 

 when the cell has lost its fluid content or protoplasm, it becomes 

 incapable of growth and of multiplication. 



The contents of the vegetal cells are normally liquid or solid. 

 Liquid they can be formed of oil or of water, holding in sus- 

 pension either molecular azotised granulations, or particles of 

 fecula, or drops of oil or of resin, or finally, small green bodies, 

 very interesting, called chlorophyllian bodies. It is to these last 

 corpuscles that the green parts of plants owe their colour. 



The liquid contents, non-oleose, are generally called protoplasm 

 by the botanists. According to certain botanists, this proto- 

 plasm is the really important part of the cell ; it secretes the 

 enveloping membranes, and the nuclei come forth from it by 

 diffe rentiation. 



In any case, this protoplasm is assuredly albuminoidal, for it 

 precipitates through the chemical agents which precipitate 

 albumine, and iodine communicates to it the yellow coloration 

 which it gives to azotised organic substances. 



The internal vesicle, the protoplasm, and the nuclei form an 

 albuminoidal whole, which Dutrochet was the first to succeed in 

 isolating, by destroying the external membrane with nitric acid 

 or dilute caustic alkalis. 



To constitute the diverse vegetal tissues, the cells assume 

 various forms. For instance, the vegetal vessels by which, espe- 

 cially in plants, the liquids and the gases circulate, are at the 

 outset formed of cells juxtaposed longitudinally. After taking 

 this linear arrangement the cells are cemented, and their walls 

 are reabsorbed at the points where there is contact. The com- 

 munication once established, the contents of the cells in their 

 turn disappear, and the canal is formed. If the vascular bundle 

 is perfect, every trace of cellular cementation completely dis- 



