136 



The Living Plant 



great many attempts have been made to determine the exact 

 function of each substance, and why it is essential. The reader 

 will be interested in the principal method used to this end. It 

 depends on the fact that there are plants, and many, which will 



grow through their whole 

 cycle from seed to seed in 

 water, without any contact 

 with soil, if only the needful 

 minerals be contained in the 

 water. This method is called 

 water culture, and the prac- 

 tical arrangements therefor 

 are well shown in the accom- 

 panying figure (figure 43), 

 while a product of the 

 method, produced in my 

 own laboratory, is shown by 

 figure 44. Now, by growing 

 one plant in water contain- 

 ing all of the necessary min- 

 erals except one, side by side 

 with another plant grown in 

 water containing all of the 



Fig. 44. — Corn plants growing by water culture needtul mmerals, it IS pOSSl- 

 in a common tumbler. The screen is ruled ^Jg ^q obsCrVe what cffcct 

 in centimeters. 



the absence of this one sub- 

 stance produces, and hence to infer what its use to the plant 

 must be. The general results of an experiment of this kind 

 are well shown in figure 43. In this way we have found that 

 potassium is necessary to the formation of the photosynthate, 

 calcium to its transfer through the plant, and iron to the 

 formation of chlorophyll (into the composition of which, how- 

 ever, it possibly enters); but further than this, and as to the 

 other materials, our knowledge is most vague and unsatisfac- 



