"250 THE MICROSCOPE AND ITS REVELATIONS. 



itself by longitudinal fission, so that each filament splits lengthways (as 

 it were) into two new ones. By the repetition of this process a mass of 

 new filaments is produced, the parts of which are at first confused, but 

 -afterwards become more distinctly separated by the interposition of the 

 gelatinous substance developed between them. Besides the ordinary cells 

 of the beaded filaments, two other kinds are occasionally observable; but 

 it has not yet been ascertained whether these are in any way subservient 

 to the true Generative act. 



248. Although many of the plants belonging to the Family Sipho- 

 nacecB attain a considerable size, and resemble the higher Sea weeds in 

 their general mode of growth, yet they retain a simplicity of structure so 

 extreme that it apparently requires them to be ranked among the Proto- 

 phytes. They are inhabitants both of fresh-water and of the sea; and 

 consist of very large tubular cells, which commonly extend themselves 

 into branches, so as to form an aborescent frond. These branches, how- 

 ever, are seldom separated from the stem by any intervening partition; 

 but the whole frond is composed of a simple continuous tube, the entire 

 contents of which may be readily pressed -out through an orifice made by 

 wounding any part of the wall. The Vauclieria, named after the Gene- 

 vese botanist by whom the fresh-water Oonfervse were first carefully 

 studied, 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 irreg- 

 ularly branching filaments, which, although they remain distinct, are 

 densely tufted together and variously interwoven. The formation of 

 motile gonidia or ' zoospores ' maybe 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 en- 

 dochrome 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 inter- 

 position 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 track is left behind it. When it meets with an obstacle, the 

 ciliary action not being arrested, the zoospore is flattened against the ob- 

 ject; and it may thus be compressed, even to the extent of causing its en- 

 dochrome to be discharged. The cilia are best seen when their move- 

 ments have been retarded or entirely arrested by means of opium, iodine, 

 or other chemical re-agents. The motion of the spore continues for about 

 two hours; but after the lapse of that time it soon comes to an end, and 

 the spore begins to develop 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 gath- 

 ered 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. 



249. Eecent discoveries have shown that there exists in this humble 



