WHAT BOTANY IS OF MOST WORTH ? 41 



of cells and tissues, and the influences controlling their 

 distribution, and also the morphological composition of 

 plants and the possibilities of great variation upon each 

 structure after it is once formed ; to know the meaning 

 of their shapes, colors, and sizes, one must know the 

 leading principles of adaptation to the external world; 

 to know how each fits its individual situation, one must 

 know the nature of irritability; to know the principal 

 kinds, one must study them by groups, and their rela- 

 tions in a system of classification. 



The most fundamental and illuminating knowledge 

 about plants must surely be that which concerns their 

 life ; yet some of its most important phases are those 

 least studied. Irritability, for example, which answers 

 in plants to sensation in animals, is, next to photo- 

 synthesis, their most important power, explaining as it 

 does how the plant directs its growing parts from the 

 very moment it bursts from the seed, how it places its 

 roots, stems, branches, leaves, flowers, and guides all its 

 movements into definite and advantageous directions. I 

 often reflect with astonishment upon the almost utter 

 neglect of this most important phase of plant-life in 

 botanical education, and this in the face of the fact that 

 its experimental study is comparatively easy. Yet many 

 other physiological phenomena of well-nigh equal impor- 

 tance are likewise neglected, and even photosynthesis is 

 often ignored. The lack of attention to ecology is not 

 unnatural in view of its comparative newness, but rich 



