CONFERVOIDE/E. 



[ 160 ] 



CONFERVOIDE^. 



the water, as in Volvox, Gonium, Syncrypta, 

 &c. The vegetable nature of these seems 

 beyond doubt. 



The Desmidiacese form another tribe of 

 very simple organization, where the indivi- 

 dual plant is composed of a single cell ; but 

 here the coat or enclosing membrane is pe- 

 cuHarly characterized by the assumption of 

 remarkable forms unlike any other vegetable 

 structures, presenting angular and escalloped 

 outlines or elegant processes projecting from 

 the wall, but always so as to exhibit a bilateral 

 symmetry. These cells are isolated,or arranged 

 in linear series or beautiful, complicated star- 

 like groups, enclosed at first in a common 

 gelatinous envelope, but readily breaking up 

 into isolated frustules. They are further 

 remarkable for exhibiting the process of 

 conjugation with great distinctness, resulting 

 in the production of peculiarly formed bodies 

 with rigid external membranes, which are 

 generally regarded, probably correctly, as 

 sporanges. They are also reproduced by 

 zoospores. 



The Diatomacese are nearly related in 

 many respects to the Desmidiaceae, but, on 

 the other hand, diverge from the ordinary 

 characters of plants so much in other re- 

 spects, that some authors place them in the 

 animal kingdom. Like the Desmidiacea;, 

 they are microscopic simple cells, isolated or 

 coherent in groups, and either free or im- 

 bedded in a definitely or indefinitely formed 

 mucous nidus. They differ, however, from 

 the Desmidiacese by possessing when free a 

 more active power of locomotion, and also 

 by being often attached by a kind of foot, 

 and this either singly or in large polypiform 

 families. Their great distinctive character 

 is the presence of a siliceous coat to the cell, 

 which preserves the form of the organism 

 when the soft parts are removed by fire or 

 acids. The cell-contents of the Diatomaceae 

 are usually of a dirty yellow colour, and this 

 appears to depend upon a modification of 

 chlorophyll. The reproduction is by division 

 and by conjugation, analogous to that of the 

 DesmidiacejE. 



The Oscillatoriaceae are truly filamentous 

 plants, the component parts of which, though 

 readily separating under external influences, 

 are organically combined into complex 

 cells in their normal state. The filaments of 

 this group are mostly very minute, and ex- 

 hibit transverse markings, which in some 

 cases are so delicate that they cannot be re- 

 garded as actual divisions of the cell-contents 

 by septa; yet the filaments break readily 



across in these places, and the fragments go 

 on growing. In the larger forms the articu- 

 lations of the cell-contents are more distinct, 

 but even here the filaments look like rows of 

 individual masses of cell-contents contained 

 in a common tube. The tube is often large 

 and gelatinous, forming a kind of sheath, 

 and in some genera the filaments are con- 

 tained in bundles in these sheaths. The 

 most remarkable point about this tribe is 

 the occurrence of the peculiar kind of motion 

 in the typical genus OsciUatoria, whence 

 they derive their name ; the filaments wave 

 backwards and forwards, and the broken 

 fragments oscillate like the beam of a ba- 

 lance, from what cause or by what means is 

 still unknown. The Oscillatoriacese are also 

 curious from the rapidity of their growth, 

 which may be readily traced under the mi- 

 croscope. 



The Siphonacese are plants of larger dimen- 

 sions and higher organization than any of the 

 preceding, and, indeed, they are placed 

 among the lower Fucoids by some authors. 

 They seem to us to be more in place here. 

 They are composed of tubular cells of much 

 larger size than those of any other Confer- 

 voids, the entire plant often consisting of 

 one undivided tube, while in other cases 

 the branches arise from true articulations. 

 In Botrydium a very cm'ious structure is 

 exhibited : the plant consists of a tough 

 membranous globule, filled with green mat- 

 ter, rising from a branched, colom-less, root- 

 like portion spreading in the damp ground, 

 the whole consisting only of one very large 

 undivided cell. In Vaucheria and Bryopsis 

 the tubular cell grows into a long filament, 

 more or less branched, but not divided. In 

 Hydrodictyon, which from its general struc- 

 ture appears referable here, the plant is 

 a large net with meshes half an inch broad, 

 the net itself being composed of large tubes 

 rounded at both ends, articulated at the in- 

 tersections of the meshes. In Codium, the 

 filaments are closely combined into a spongy 

 mass. The fructification of these genera is 

 very varied, so that the group appears 

 scarcely natural ; but the plants are all more 

 or less anomalous, and have affinities with 

 very different tribes, while the comjjaratively 

 enormous cells of which they are composed 

 are peculiar to them among the filamentous 

 Confervoids. Vaucheria is reproduced by 

 very large oval spores covered with innumer- 

 able vibratile cilia, by means of which they 

 swim actively in water ; the spores are de- 

 veloped from the contents of the ends of the 



