SIPHOXACEiE : ZOOSPORES OF VAUCHEEIA. 325 



centre, and sometimes at intervals along their whole length), -which 

 are destitute of Endochrome, and are sometimes furnished with 

 cilia; and 'sporangial cells,' which seem like enlarged forms of the 

 ordinary cells, and which are usually found in the neighbourhood of 

 the preceding. It has been supposed that the ' vesicular cells ' are 

 'antheridia' or sperm-cells, producing 'antherozoids,' and that 

 the ' sporangial cells ' contain germs, which, when fertilized by the 

 antherozoids, and set free, become 'resting-spores,' as in certain 

 members of the family to be next noticed. 



245. Although many of the plants belonging to the Family 

 Siphonacece 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 Protophytes. 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 arborescent frond. These branches, however, 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 Vaucheria, named 

 after the Grenevese botanist by whom the Fresh-water Confervse 

 were first carefully studied, may be selected as a particularly good 

 illustration of this family ; its history having been pretty com- 

 pletely made out. Most of its species are inhabitants of Fresh 

 water ; but some are Marine ; and they commonly present them- 

 selves 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 motile gonidia or 'Zoospores' may be readily observed in these 

 plants, the whole process us rally 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 invest- 

 ing 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 

 coloured 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 object; and it may thus be compressed, even 



