314 MICROSCOPIC FORMS OF VEGETABLE LIFE. 



the entire contents of which may be readily pressed out through 

 an orifice made by wounding any part of the wall. The Vau- 

 cheria, named after the Genevese botanist whose admirable re- 

 searches on the fresh-water Confervse have been already referred 

 to (p. 38), may be selected as a particularly good illustration of 

 this family ; its history having been pretty completely made out. 

 Most of its species are inhabitants of fresh water ; but some are 

 marine, and they commonly present themselves in the form of 

 cushion-like masses, composed of irregularly branching filaments, 

 which, although they remain distinct, are densely tufted together, 

 and variously interwoven. The formation of moving gonidia or 

 "zoospores" may be readily observed in these plants, the whole 

 process usually occupying but a very short time. The extremity 

 of one of the filaments usually swells up in the form of a club, 

 and the endochrome accumulates in it, so as to give it a darker 

 hue than the rest ; a separation of this part from the remainder 

 of the filament, by the interposition of a transparent space, is 

 next seen ; a new envelope is then formed around the mass thus 

 cut off; and at last the membranous wall of the investing tube 

 gives way, and the "zoospore" escapes, not, however, until it 

 has undergone marked changes of form, and exhibited curious 

 movements. Its motions continue for some time after its escape, 

 and are then plainly seen to be due to the action of the cilia with 

 which its whole surface is clothed. If it be placed in water in 

 which some carmine or indigo has been rubbed, the colored 

 granules are seen to be driven in such a manner as to show that 

 a powerful current is produced by their propulsive action, and a 

 long tract is left behind it. When it meets with an obstacle, the 

 ciliary action not being arrested, the zoospore is flattened against 

 the object; and it may thus be compressed, even to the extent 

 of causing its endochrome to be discharged. The cilia are best 

 seen, when their movements have been retarded or entirely ar- 

 rested by means of opium, iodine, or other chemical reagents. 

 The motion of the spore continues for about two hours ; but after 

 the lapse of that time it soon conies to an end, and the spore 

 begins to develope itself into a new plant. It has been observed 

 by linger, that the escape of the zoospores generally takes place 

 towards 8 A.M. ; to watch this phenomenon, therefore, the plant 

 should be gathered the day before, and its tufts examined early 

 in the morning. It is stated by Dr. Hassall, that he has seen the 

 same filament give off two or three zoospores successively. Their 

 emission is obviously to be regarded as a method of increase by 

 gemmation, rather than as a generative act ; and recent disco- 

 veries have shown that there exists in this humble plant a true 

 process of Sexual Generation, as was, indeed, long ago suspected 

 by Vaucher, though upon no sufficient grounds. The branching 

 filaments are often seen to bear at their sides peculiar globular 

 or oval capsular protuberances, sometimes separated by the in- 

 terposition of a stalk, which are filled with dark endochrome ; 



