i6 



THE PLANT WORLD. 



dry weights of the tops and the dry weight of the roots may be 

 taken as additional criteria of growth. 



The method here described may be used for studies of the 

 nutrient or stimulating value of various substances. A striking 

 illustration of the value of the endosperm to the young seedling 

 may be presented by making two cultures in the same solution, the 

 seedlings of one culture having had the seeds removed at the 

 time of setting up. while those of the other are normal. A 

 single example to illustrate the kind of results which may be ob- 



FlG. 3. 



tained is given in Fig. 3. No. i is in pure water, No. 2 in a 

 Knop's nutrient solution containing 112 parts per million (0.0112 

 per cent.) of total salts. The succeeding cultures have the same 

 nutrient solution, each one being twice as concentrated as the pre- 

 ceding one of the series. It is seen that the optimum strength lies 

 in the range of concentrations from 224 to 14336 parts per mil- 

 lion ( Nos. 3 to 9 in the figure), and that variations in concentra- 

 tion within these limits do not markedly effect the growth of the 

 plants. The solution in No. 10. containing 28672 parts per mil- 

 lion of total salts, is obviously too strong for the plants. 



