THE WONDERS OF LIFE 



or expansibility of the plant-cells. This is effected by 

 the osmotic pressure of the internal cell-fluid and the 

 elasticity of the cellulose wall, which is thus expanded. 

 Nevertheless, in both cases — ^^and in all "vital" phenom- 

 ena — the real cause of the process is, in the ultimate 

 analysis, the chemical play of energy in the active plasm. 



The metaphyta, with few exceptions, are fixed in one 

 spot for life, or only mobile for a short time when they 

 are young. In this they resemble the lower metazoa, 

 the sponges, polyps, corals, bryozoa, etc. They have 

 not free locomotion. The motor phenomena which we 

 find in them affect only special parts or organs. They 

 are mostly reflex or paratonic, and due to external 

 stimuli. Only a few of the higher plants exhibit autono- 

 mous or spontaneous movement, the stimulating cause 

 of which is unknown to us, and which may be compared 

 to the apparently voluntary actions of the higher ani- 

 mals. The lateral feather-leaves of an Indian butter- 

 fly flower (hedysarum gyrans) move in circles through 

 the air, like a pair of arms swinging, without any exter- 

 nal cause; they complete a circle in a couple of minutes. 

 Variations in the intensity of light have no effect on 

 them. Similar spontaneous movements of the leaves 

 of several species of clover (trifolium) and sorrel (oxalis) 

 are performed only in the dark, not in the light. The 

 terminal leaf of the meadow-clover repeats its rotation, 

 which describes more than one hundred and twenty de- 

 grees of an arc, every two to four hours. The mechani- 

 cal cause of these spontaneous "variation movements" 

 seems to lie in variations of expansibility. 



Voluntary and autonomous turgescence-movements 

 of this kind are only observed in a few of the higher 

 plants, but stimulated movements that are accomplish- 

 ed by the same mechanism are very common in the 

 vegetal world. We have, especially, the well - known 

 "sleep," or nyktitropic movements, of many plants. 



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