508 ORGANOLOGY. 



even they absorb sometimes one kind of matter and sometimes another. 

 This is not exhibited at all in the form of the species of the plant, for this 

 remains the same in all circumstances. The change takes place in indi- 

 vidual cells. Thus, in the same cellular mass, say of 1000 cells, there 

 will be in one case 200 containing starch granules, and 400 containing 

 oil ; in another there will be 500 containing starch, and only 100 oil : 

 but the form of the plant suffers not the slightest change ; or, what is 

 more frequently the case, the relative quantity of particular substances 

 becomes changed : thus, particular cells will at one time contain 7 per 

 cent, of gluten and 70 per cent, of starch, and at another time will con- 

 tain 35 per cent, of gluten and 40 per cent of starch. For every species 

 of plant there are definite quantities of certain matters necessary for its 

 existence, but it frequently takes up matters which are not necessary 

 for its existence, and a superfluity of matters which are necessary for its 

 existence ; and thus both the quantity and quality of its contents are 

 changed. This, then, is a problem for pure empirical research how far 

 plants will bear departures in the quality and quantity of the normal 

 constituents of their food. Many plants appear to require a very pre- 

 cise diet, which will account for their limited distribution and the diffi- 

 culty of their culture, whilst others seem to adapt themselves to all 

 circumstances, and present great variety in their contents. Thus the 

 composition of the milky juice of the Papaver somniferum (Opium), 

 according to Biltz, Mulder, and Schindler, is as follows : 



In Morphia, from 2-842 to 20-00 per cent 

 Narcotin 1-30 33-00 



Caoutchouc 2-00 6-012 



It is also well known that the plants which yield caoutchouc afford 

 very variable quantities, according to the varying circumstances under 

 which they grow. If we also add to this the fact that plants yield 

 poisonous or inert secretions according to their locality, we cannot but 

 conclude that certain substances appear or disappear in the plant when 

 external circumstances are given, without altering their external cha- 

 racter. This great variability in the composition of plants must always 

 be regarded in experimenting upon the vegetable kingdom, . 



IV. External Conditions of the Absorption and Assimilation 



of Food. 



202. As external conditions of the absorption and assimilation, 

 we may here point out : 



I. The soil in which the plants root. This requires, besides its 

 chemical contents of inorganic matter for food, also certain me- 

 chanical and physical properties in order to render the nutrition of 

 plants possible. Hence clay and humus, as substances that absorb 

 gas and vapour, are important. 



Next to the consideration of the materials themselves of the food of 

 plants, in order to form a true theory of the culture of plants, and the 

 understanding the processes of nutrition, there is nothing so important 

 as the investigation of those relations upon which the health of the plant 

 is essentially dependant, and which do not afford the materials of the 



