92 BIOLOGY. [Book ii. 



cold which arrests this gyratory movement, we can by beating 

 the soil put the liquid again into motion. ^ 



With respect to this manifest action of heat it is curious to 

 see that light seemingly influences little or not at all the pro- 

 toplasmic movement which is accomplished without apparent 

 modification even when the plant is kept in darkness. 



After gyrating in the cells, travelling in the vessels and the 

 meatus, after taking from or giving to the elements, which it 

 has traversed or passed beside, certain of the matters which it 

 conveys, the sap arrives at the pai-t truly aerian of the vegetal. 

 There it undergoes very important modifications, thanks to the 

 special action of a substance of which we have now to speak. 

 This substance is the green matter of the leaves, the chlorophyll. 



2. — Chlorophyllian Property. 



Chlorophyll is the substance to which all the green parts of 

 plants owe their colour. In the cells of certain lichens and of 

 certain algse, the chlorophyll sometimes presents itself in the 

 amorphous state, colouring all the protoplasm, sometimes in irre- 

 gular masses ; but habitually in all the vascular plants it has a 

 definite form, that of green granulations of from O""", 001 to 

 0""°, OOS in diameter, of homogeneous appearance and without 

 nuclei. We can obtain from this green matter fat crystallisable 

 bodies, stearine, margarine and so on, and an immediate azotised 

 principle, chlorophyll properly so called, the elementary analysis 

 of which gives oxygen, hydrogen, azote, carbon, and iron. By 

 an appropriate chemical treatment Fremy was able to separate 

 chlorophyll into two substances ; the one yellow, phylloxanthim, 

 and the other blue, phyllocyanine. 



Chlorophyll rises spontaneously in the cellular protoplasm. 



First of all are formed colourless or yellow pai-ticles, which 



grow green afterwards, if the cell in which they ar« contained 



is exposed to the light. The chlorophyllian particles, bom in 



' Nageli, quoted by Sachs, TraiU de Botanique,-^^. 855, 856. 



