36 THE TEACHING BOTANIST 



yoked with preceding factors, combined with a desire 

 to learn what these are. For the cultivation of this 

 instinct of causation, anatomy and morphology should, 

 from the first, be viewed in the light of the factors 

 determining them, that is, they should be approached 

 through physiology and ecology. It is an important 

 and valuable discipline to study the exact way in 

 which leaves are built, and to learn their diverse 

 forms and special modifications ; but only a fraction 

 of the value of this study is realized unless it is made 

 in the spirit of constant inquiry, which asks why they 

 are flat, and horizontal, and thin, and greener on the 

 upper than on the lower surfaces, and why they have 

 become compounded or altered to spines or provided 

 with stipules. It is not, however, enough to simply 

 ask these questions ; the habit of actively seeking the 

 answers to them must be inculcated. And the answers 

 come in part through observation, but more through 

 experiment. Indeed, so important a factor is experi- 

 ment in elucidating causation that one may almost 

 speak of the causative instinct and the experimental 

 instinct as synonymous. The cultivation of the habit 

 of testing the connection of causes and effects by 

 experiment is therefore a most important part of 

 botanical training. An experiment is a definite ques- 

 tion asked of nature, and properly follows after all 

 possible observation and reflection, and is most often 

 a testing of possible hypotheses suggested by this 



