190 



BOTANY 



I'AKT I 



potassium participating in the most important synthetic processes of 

 plants, is found in combination with various acids, particularly in 

 reservoirs of reserve material (in seeds to the extent of 2 per cent) 

 and in growing points (in leaves only | per cent). CALCIUM also is 

 taken up in the form of one of its abundant salts, and in considerable 



quantities (2-8 per cent). Calcium 

 plays an important part in the meta- 

 bolic processes of plants, as a vehicle 

 for certain other essential substances, 

 and, as a means of fixing and rendering 

 harmless hurtful bye -products (oxalic 

 acid) ( 13 ). IRON, although of the greatest 

 importance in the formation of chloro- 

 phyll, is present in plants only in 

 small quantity. 



In order to determine the nutritive 

 value of different substances the method 

 of WATER-CULTURE has proved particu- 

 larly useful (Fig. 183). In these cul- 

 ture experiments the plants, grown 

 either directly from the seed or from 

 cuttings, are cultivated in distilled 

 water to which have been added certain 

 nutritive salts. The distilled water 

 must not have been stored in a copper 

 vessel, and the salts must be chemically 

 pure. If all the essential nutritive salts 

 are present in the culture solution, even 

 larger plants, such as Indian Corn, 

 Wheat, Beans, etc., will grow to full 

 strength and mature seeds as if grown 

 in earth. It is not necessary in these 

 experiments to provide carbon com- 

 pounds in the nutrient solution, as 

 plants do not derive their carbon supply 

 FIG. m.-water-cuitures of Fagopyrum through their roots, but, by the help 

 rscuientitm, i. iii nutrient solution of their leaves, from the carbonic acid 



containing potassium ; //., in nutrient Q f ^g atmosphere. 



solution without potassium. Plants _,, , - 



reduced to sain.- scale. (After XOBBE.) -I- he young plants grow tor a 



time just as well in pure distilled 



water as in the nutrient solution ; but as the supply of nourishment 

 stored in the seeds becomes exhausted, they gradually cease to 

 grow, and die. If one of the essential constituents of plant food be 

 omitted from the nutrient solution, although the young plants 

 will grow better than in the distilled water, they in time become 

 abnormally developed. When, for example, a plant is grown in a 



