BOTANY 157 



in the method of study of the two sciences,* more marked in 

 early stages of development of the sciences than now, and 

 even yet expressing itself in differences in the elementary 

 teaching of the two subjects. I refer to the fact that much 

 can be learned of the functions of the various organs of ani- 

 mals by direct observation, but not so with plants. It re- 

 quires only the most superficial observation to know that the 

 stomach takes care of food, that the lungs are for breathing, 

 the eyes for seeing. Even the one-celled Paramecium has a 

 special organ for taking in food and the Amceba flows 

 around a dainty morsel in a way that can actually be seen. 

 But who could tell, by mere observation, how the Pleurococcus 

 vulgaris takes in food through a completely closed membrane, 

 or what acuteness of mere observation would reveal the fact 

 that foliage leaves are the stomachs, and not, as is so gen- 

 erally and so erroneously supposed, the lungs of plants? The 

 observation of centuries failed to reveal the organs by which 

 plants detect the direction and intensity of light-rays. Largely 

 for this reason the study of plant functions developed much 

 later than the study of plant structures, while in the study of 

 animals, especially of man, physiology developed along with 

 anatomy. 



Moreover, in botany a refinement of observation becomes 

 necessary. We must often know all of the circumstances 

 under which we observe, and make our observations under 

 various combinations of circumstances, now with one con- 

 dition present, again with it absent, always altering but one 

 condition at a time. This processs is called experimentation. 

 In simple observation, conditions are taken as they are found, 

 complex, and not always carefully analyzed. Experimenta- 

 tion is observation under predetermined and known condi- 

 tions, with an attempt to take account of all the factors in- 

 volved. It is absolutely necessary in order to learn the most 



*Sachs. J. Hist. Bot., Eng. trans, by Garnsey and Balfour. 

 Oxford, 1906. p. 360. 



