Chap, v.] CONSTITUTION OF ORGANISED BODIES. 43 



suspends them. The reason is that the vital activities and pro- 

 perties are directly and solely derived from the physico-chemical 

 properties in the midst of the anatomical elements. Consequently 

 we see them grow stronger, or languish, vanish, reappear, or 

 hasten- to final extinction, from the sway of the molecular move- 

 ments and mutations of which they are the expression. 



2. Histology of Plants. 



The vital functions are less numerous, less specialised in the 

 plant than in the animal, it being understood of course that we 

 except the most inferior organisms in the two kingdoms. We are 

 therefore justified in supposing, h. priori, a less sharp specialisa- 

 tion in the form of the elements. This is what is actually the 

 case. "Wliile in the superior animal we find varied histological 

 types very clearly distinguished from each other ; in the plant, 

 on the contrary, the elementary forms are less decided, less dis- 

 similar, and sometimes they can be supplemented physiologically. 



It is from the microscopical anatomy of plants that has sprung 

 the cellular theory, so contested at present in France, but gene- 

 rally admitted in Germany, and according to which every ana- 

 tomical element, vegetal or animal, has as direct origin a simple 

 cell. In effect, in the vegetal world, the utricular, the cellular 

 type greatly predominates. Every plant, from the simplest to 

 the most complex, is formed by an aggregation of cells, or of fibres 

 manifestly originating in cells. 



Every complete anatomical vegetal element is a cell formed of 

 a double wall, of a content, and of one or more nuclei. 



The external cellular envelopment is constituted^ chemically, 

 by a ternary substance united to certain salts ; this is the cellu- 

 lose, composed of carbon, of hydrogen, and of oxygen. The 

 chemical formula of the cellulose is analogous to that of sugars. 

 It is C'2 H'^O^". When the histological element is complete, this 

 external membrane is interiorly lined with another very thin 

 vesicle ; but the second contains azote : it is albiuninoidal. This 

 azotised membrane englobes a semi-liquid substance and one or 



