CHAPTER II 



METHODS OF WORKING 



I. Discussion of Methods. 



In the course of the scattered investigations on plant poisons and 

 stimulants, various experimental methods have been brought into use, 

 but these all fall into the two main categories of water and soil cultures, 

 with the exception of a few sand cultures which hold a kind of inter- 

 mediate position, combining certain characteristics of each of the main 

 groups. 



The conditions of plant life appertaining to soil and water cultures 

 are totally different, so different that it is impossible to assume that a 

 result obtained by one of the experimental methods must of necessity 

 hold good in respect of the other method. A certain similarity does 

 exist, and where parallel investigations have been carried out this 

 becomes evident, but it seems to be more or less individual, the plant, 

 the poison and the cultural conditions each playing a part in determin- 

 ing the matter. 



1. Water cultures. 



This method of cultivation represents the simplest type of experi- 

 ment. Its great advantage is that the investigator has absolute control 

 over all the experimental conditions. Nutritive salts and toxic substances 

 can be supplied in exact quantities and do not suffer loss or change by 

 interaction with other substances which are beyond control. Any pre- 

 cipitates which may form in the food solution are contained within the 

 cultur&'iessel and are available for use if needed. The results are thus 

 most useful as aids in interpreting the meaning of those from the field 

 experiments, the results of the one method frequently dovetailing in with 

 those of the other in a remarkable way. The disadvantage of the water 

 culture method is that it is more or less unnatural, as the roots of the 

 plants are grown in a medium quite unlike that which they meet in 



