254 COMPENDIUM OF GENERAL BOTANY. 



fungi (rhizobia) capable of assimilating free nitrogen, but also non- 

 leguminous plants, as opposed to the conclusions of Helleiegel. 



We will now return to the important nitrogen-bearing com- 

 pounds. According to Boussingault, phanerogams appropriate 

 nit/'ic acid more readily than they do ammonia ; for some fungi am- 

 monia is better suited than nitric acid (Pasteue, A. Mayer, 

 Nageli). 



Sulj^hur a.Tid phosphorus enter the plant in the form of sulphates 

 and phosphates.' 



The two binary compounds CO, and H^O supply the plant with 

 the elements C, O, and H. CO, is almost exclusively taken from 

 the atmosphere, H,0 almost exclusively from the soil. The process 

 of assimilating CO, and H,0 necessitates the presence of chloi-ophyll 

 and the aid of sunlight. For each volume of CO, assimilated there 

 is liberated an equal volume of O. The most common product of 

 assimilation among dicotyledons is starch (amylum), which occurs in 

 the form of small grains. If we consider CgHj^O^ as the formula 

 for this compound, the reaction may be represented as follows : 



6C0, + 5H,0 = C.H,„0, + 120. 



In other instances (many monocotyledons) a form of sugar seems 

 to take the place of the starch (see pp. 122 and 131). 



So far we have not been able to follow the process of assimilation 

 in its various phases. In the circulation of food-substances within 

 the plants, the processes of catabolism, such as converting starch and 

 cellulose into sugar, decay, etc., are much better known than the 

 processes of metabolism (assimilation and various processes of 

 transformation. (See p. 258). 



At present we have not a clear understanding of the part that 

 chlorophyll plays in the process of assimilation. In the discussion 

 of the assimilating system we learned that the influence of light 

 varied with the wave-lengths (color) ; this relation was made clear 



' According to Sachs, the following is a very satisfactory culture-fluid for 

 plants: 



AVater 1000.0 cu. c. 



Potassium nitrate .. . , 1.0 gram. 



Chloride of sodium .5 " 



Sulphate of calcium .5 " 



Sulphate of magnesium .5 " 



Phosphate of lime (finely pulverized) .5 " 



Chloride of iron a few drops. 



