SPONTANEOUS MOVEMENTS IN PLANTS. 349 



(Fig. 89, 636). Immediately on its discharge from the mother 

 plant the spore begins to move freely in the water, and continues to 

 do so for some hours, when it fixes itself and begins to grow (Fig, 

 638). Its movements, moreover, like those of the antheridial fila- 

 ments or corpuscles, may be enfeebled or arrested by the application 

 of a weak solution of opium or chloroform. Through these means 

 it has been ascertained that they are caused by the vibrations of 

 minute cilia which cover the surface, which are rendered visible 

 by thus enfeebling their movement, and which exhibit the closest 

 resemblance to the vibratile cilia of animals, especially those of the 

 polygastric animalcules. In the Conferva tribe generally the vibra- 

 tile cilia occupy one end of the spore, and are in some cases numer- 

 ous (as in Fig. 644), in others only two or three in number. The 

 spores are small, and of about the same specific gravity as the water 

 in which they live, so that a slight force sufiices to propel them. 



679. Locomotion of Adult Microscopic Plants. The spores of Vau- 



cheria and the like, becoming quiescent before germination, grow 

 into fixed thread-like plants of considerable size, endowed with no 

 greater degree of motivity than ordinary vegetables. A multitude 

 of still simpler Algae, however, swarm in every pool or stream, so. 

 minute in size as to be individually totally invisible to the naked, 

 eye (most of them when full grown are very much smaller than the 

 spores of Vaucheria, &c.) ; and these are endowed, even at maturity, 

 with such powers of locomotion that their vegetable character, 

 although now well made out, was long in question on this account 

 alone. Of this kind are the various species of Oscillaria (Fig. 84), 

 so named from the writhing movement they exhibit, the Desmidi- 

 acea3, to which Closterium (Fig. 631) belongs, and the nearly 

 allied Diatomacese, — the lowest, minutest, and the most freely 

 moving of plants, but clearly members of the vegetable kingdom 

 notwithstanding. These execute free movements of translation, in 

 some cases slow, in others rapid; but the mechanism of the motion 

 is still unknown. 



680. Not only, therefore, do plants generally manifest impressi- 

 bility or sensitweness to external agents, and execute more or less 

 decided, though slow, movements ; but many species of the higher 

 grades exhibit certain vivid motions, either spontaneous or in conse- 

 quence of extraneous irritation ; while the lowest tribes of aquatic 

 plants, as they diminish in size and in complexity of organization, 

 habitually execute, at some period at least, varied spontaneous move- 



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