CONFERVOIDE.E. 



[ 161 ] 



CONFERVO1DE.E. 



filaments ; another mode of reproduction is 

 also stated to exist, in which a process of 

 conjugation is said to occur ; this is spoken 

 of elsewhere. In Hydrodictyon the repro- 

 duction takes place by the conversion of the 

 contents of the cells into numerous zoo- 

 spores, which * swarm' inside the cell, and, 

 never escaping, arrange themselves on the 

 walls in the form of a network, acquire mem- 

 branes, and, by the solution of the cell-wall, 

 emerge as new, perfect, net-like fronds, like 

 the parent. In Bryopsis the contents of the 

 ends of the filaments are developed into nu- 

 merous small zoospores,with two or four cilia, 

 like those of the Confervaceae ; these escape 

 and germinate, and produce filaments. In 

 C odium, the ovoid lateral sacs, ordinarily re- 

 garded as spores, also produce numerous 

 zoospores with two cilia, which escape and 

 germinate in like manner. In the anomalous 

 genus Achlya, which, from the colourless 

 condition of the contents and the parasitic 

 habit, is almost like a Fungus, the reproduc- 

 tion resembles that of Bryopsis, zoospores 

 being developed and emitted from the ends 

 of the tubes, germinating and growing into 

 filaments with great rapidity. 



The Confervaceae and Zygnemacese are in- 

 teresting families of this order, known as the 

 Silk-weeds so abundant in ponds, ditches, 

 and running fresh water, and also occurring 

 in brackish water and the sea. They are 

 simple plants, composed of cylindrical cells, 

 flattened at the top and bottom, of variable 

 length in proportion to their diameter, ar- 

 ranged in lines so as to form long threads, 

 which are simple or give off lateral branches 

 of like structure. They are not very evi- 

 dently gelatinous, but they are often slip- 

 pery to the touch, and the microscope mostly 

 detects a delicate gelatinous coat investing 

 the filaments, which consists in reality of the 

 softened older external walls in course of 

 solution. The cells or joints are filled with 

 contents, usually of green, but occasionally 

 of brown or purple colour, either lining the 

 walls equally or arranged in various patterns, 

 such as spiral coils, reticulations, &c. upon 

 them. They are reproduced by spores and 

 by zoospores, and in the production of the 

 former a very curious process takes place in the 

 Zygnemaceae; in Zygnema (fig. 137, page 166) 

 and others the filaments become coupled by 

 cross tubes, produced by the inosculation of 

 branches sent from two cells of adjacent 

 filaments; the contents then become inter- 

 mixed and produce a spore, which acquires 

 a thick coat, and remains at rest for some 



time, then germinates, and forms a new fila- 

 ment. In CEdogonium, spores are formed 

 in certain stages from the entire contents of 

 joints, apparently without conjugation ; these 

 sometimes acquire a red colour. The zoo- 

 spores vary in different genera; in CEdogo- 

 nium they are very large, being formed 

 from the entire contents of the cell, and 

 instead of a pair of cilia, or four, they bear a 

 crown of cilia at the apex. In most cases, 

 however, they are produced in large numbers 

 in each cell, and are small, pear-shaped, and 

 furnished with two cilia, as in Cladophora, 

 Conferva, Chcetomorpha, &c. They certainly 

 occur in some cases in the Zygnernaceae, and 

 from what is seen in CEdogonium, it seems 

 probable that they are normal there. They 

 escape either by orifices formed in the cell- 

 wall (Chcetomorpha], by an annular dehis- 

 cence of this ((Edoaonium), or by the fila- 

 ments breaking up entirely (Conferva). 



The Chaetophoraceae differ from the Con- 

 fervaceae principally in their habit and mode of 

 branching. They occur in the sea and in 

 fresh water, and are characterized by the 

 presence of a jelly enveloping the filaments, 

 or branched, round, or shapeless masses 

 composed of filaments ; by the cells consti- 

 tuting the joints of the filaments bearing 

 slender bristle-like branches ; and frequently 

 by the collection of the green contents in 

 the middle of the cells. They are repro- 

 duced by zoospores, either numerous or soli- 

 tary in the cells, bearing four cilia. 



The Batrachospermeae exhibit a greater 

 complexity of structure, consisting of jointed 

 moniliform filaments, composed of rows of 

 cells, branched and bearing whorls of ramuli; 

 the filaments of the whorls dense, dichoto- 

 mous, and beaded, some of them growing 

 down over the central filament, and forming 

 a sheath round it. The fructification con- 

 sists of spore-like bodies borne on the fila- 

 ments of the whorls, but their true nature 

 has not yet been investigated. The plants 

 are brownish-green or purplish, and occur 

 in fresh water. 



The Lemaneeae are freshwater Algae, by 

 some supposed to bear a close relation to 

 the lower Fucoids, occurring in rapid rivers, 

 attached to stones. The fronds are branched 

 and of leathery texture, consisting of tubes 

 composed of cellular tissue, the superficial 

 layers small, polygonal, and firmly conjoined, 

 the deeper layers bounding the cavity of the 

 tubes lax and spherical. The fructification 

 consists of beaded filaments arising from the 

 internal cells, and growing out freely in the 



M 



