412 VEGETABLE PHYSIOLOGY 



differences in hygrometric condition, though nothing 

 anatomical suggests such diverse powers. If such a sensi- 

 tive organ is acted upon at the same time hy two stimuli 

 which usually produce opposite movements, the resulting 

 position is always such as would be caused by the greater 

 influence of the stronger of the two. The organ is, in fact, 

 able to receive both stimulations simultaneously, and to 

 respond to each as if the other were not received. 



If we turn to the second feature of the nervous system, 

 we find that the motor mechanism of the plant seems at 

 first to be entirely different from that of the animal. 

 Closer consideration, however, lessens the difference con- 

 siderably. The motor mechanism of an animal is nearly 

 always either muscular or glandular. The vegetable 

 cell seems to have much more in common with the gland 

 cell of an animal than with its muscles. Stimulation of a 

 nerve going to a gland frequently causes a flow of liquid from 

 the latter, probably owing to a change in the permeability 

 of the protoplasm of the gland-cells. The contractile 

 power is but little developed in vegetable protoplasm, and 

 when present it seems to be rather passive than active, 

 to be associated with recoil rather than true contraction. 

 Still, the latter is not entirely absent. We have seen that 

 it can be detected in the pulsation of vacuoles, in ciliary 

 motion, and in the crawling movements of the Myxomycetes. 



Though the power of contraction is comparatively 

 seldom found, the action of the gland-cell is recalled by the 

 power which vegetable protoplasm possesses of resisting or 

 assisting the transit of water. The effect is really similar in 

 both cases ; in the animal the disturbance to the protoplasm 

 leads to a contraction of its substance, in the plant to its 

 lessening its resistance to the passage of water through 

 it. Each protoplasm responds in its own appropriate 

 fashion, which is based upon the need of the organism of 

 which it is part. The main requirement of most animals 

 is freedom of locomotion or rapid assumption of new posi- 

 tions by the body. The most important duty of the plant is 



