IX.] THE DYNAMICS OF LIFE. 103 



any physical property, or by any extraneous influences. 

 These movements are most remarkably shown at times in 

 the spaces of young cellular tissue. The movement termed 

 rotation, or gyration, which is often seen in the contents of 

 young cells, and which, in some form or other, is probably 

 of general occurrence, may depend on the contractility ^ of 

 protoplasm. They are said by those who have studied 

 them to present a close resemblance to those of Amceba ^ 

 and its allies. No one has yet shown a distinction of 

 importance between protoplasm of the vegetable and sar- 

 code of the animal kingdom. But there are other move- 

 ments in plants, the cause of which is less equivocal. 

 Such movements are not confined to the lowest plants, as 

 the Oscillatorise, but are met with among the most highly 

 organized members of the vegetable kingdom. The move- 

 ments of sensitive plants, various species of Mimosa, of 

 Dionaea muscipula,^ of certain tropical species of Desmo- 

 dium, of the stamens of Barberry, &c. can be referred only 

 to vital contractility of certain of their tissues. Whatever 

 obscurity may hang over these, let it be remarked that 

 there is the same evidence of the nature of this vital con- 

 tractility in plants as in animals. It is dependent on life, 

 and not, like any physical property, retained so long as 

 the structure itself is not destroyed. So, also, these move- 

 ments either occur spontaneously, or may be excited by 

 various stimuli — touch for example. If those motions 

 depended upon elasticity, or hygroscopic changes, or any 

 other physical cause which elsewhere operates, how could 

 stimuU act to produce them? Moreover, they appear to 

 be governed by the same laws that regulate their action in 

 the animal kingdom. Their energy varies with the vigour 

 of the plant. Excessive exercise produces exhaustion, hut 

 the power is restored during subsequent repose. This evi- 

 dence, thus clear and satisfactory, receives a remarkable 



1 Contractility is not a good word. What is meant is only the tendency 

 to spontaneous motion. 



2 The amoeba is an animal, and one of the simplest known, being a 

 minute gelatinous mass without structure. 



^ Familiarly called " Venus's fly-trap," from the way in whioh the 

 leaves spontaneously close on flies and crush them. 



