AN OUTLINE OF PIIYTOBIOLOGY. I 



the more difficult by the fact that cross-fertihzation being 

 absolutely more advantageous than self-fertilization in 

 nature in the struggle for existence, it has to be 

 provided that the carrying of the pollen shall be to 

 the stigma of another plant. Hence come the adapta- 

 tions to cross-fertilization, resulting in the formation 

 of the flower, with its colors, odor, nectar and varied 

 forms, the whole aftording us the most splendid example of 

 adaptation to be found in the vegetable kingdom. This 

 division of locomotion is, however, so large and important 

 that although it belongs logically in the present paper it 

 must receive separate treatment, and it will be considered 

 in a future paper of this series along with " adaptations to 

 reproduction ; " at present we devote our attention to 

 locomotion of plants as scattering them through space. 



Let us understand clearly the mechanical problem in- 

 volved. A piece of matter endowed with life, and having 

 isize and weight, must be moved through a considerable 

 iSpace in such a manner as not to injure it. Only a very 

 limited movement can be eifected by the plant itself, so 

 that in the vast majority of instances the movement must 

 l)e efl:'ected by outside agencies. How, then, can the 

 plant effect movement, and what are the forces in nature 

 outside of the organism capable of moving ponderable 

 matter ? 



The former can occur through 



I. Independent animal-like movement. 

 II. Extension away of parts by growth. 



III. Locomotion by movements of ripening tissues. 



The latter are 



IV. Currents of air. 

 V. Currents of water. 



VI. Movement of animals. 

 VII. Gravitation. 



