THE VICTORIAN NATURALIST. 85 



bodies escape and swim by means of cilia, but fail to develop 

 independently. Uniting in pairs however, they form a body 

 which attaches itself, and develops into a plant of small 

 growth, which in turn gives rise to other plants, similar in most 

 respects to the parent. This is a sexual form of reproduction. 

 Of the Zygnemacese the genera Spirogyra and Zygnema exhibit 

 sexual reproduction. In some cases two cells of adjacent filaments 

 bulge out their walls in processes which meet, and the common 

 wall formed by the meeting of the processes dissolves, and there is 

 formed a tube connecting the two cells. Through this tube one 

 cell, which, on account of its active character, is considered the 

 male, and called a gamete, flows through into the cell in the other 

 filament. There the two cells fuse together their protoplasm and 

 contained chromatophores, the process usually taking place in 

 the dark, and occupying a considerable time, in one case which 

 I watched, over three hours, but I believe that Mr. J. Shephard 

 has found it, under other circumstances, to be completed in less 

 than an hour. After fusion the newly-formed body puts on a 

 firm membrane, and lies more or less loosely in the cell chamber. 

 It is then called a zygote, or fertilized oospore. It turns from 

 green to reddish-brown, and rests until conditions are favourable, 

 when the cell wall bursts open at one end, and the contents 

 emerge in the form of a club-shaped, delicate green body, which 

 lengthens and transversely divides to form a filament of cells as 

 in the parent. There are instances, however, of sexual elements 

 which, disappointed at pairing time, make the best of their mis- 

 fortune, and develop into new plants from the cell chambers in 

 which they have been left behind. This may be found in 

 Hormiscia zonata, as described by Cooke. 



Although the species of many Algae cannot be determined 

 satisfactorily without the process of reproduction being known, 

 still there are some having peculiarities of shape and disposition 

 of chromatophores and pyrenoids which make the genus easily 

 recognizable, examples being Spirogyra, with parietal spiral 

 bands ; Zygnema, with twin star-shaped bodies ; and Mougeotia, 

 with a single axile plate ; and also many Desmids of conspicuous 

 beauty and shape ; while in the abrupt spheroidal swellings in the 

 filaments of the Giidogoniacese, with the characteristic parallel 

 transverse striae of certain cells, the guide to the determination of 

 the genus may be found, though the fruit may not be sufficiently 

 matured to fix the species. 



In the higher group, Characeae, the genus Chara may, in the 

 absence of fruit, be easily distinguished from Nitella by certain 

 differences, which will be referred to later. 



Many of the fresh-water Algse exercise certain movements, both 

 of the whole plant, as in some Desmids, Volvox, and species of 

 the family Lyngbyae, or of parts of the internal structure of the 



