570 MICROSCOPIC FOEMS OF VEGETABLE LIFE THALLOPHYTES 



division of the original cell. A certain portion of the ectoplasm 

 seems to undergo increased nutrition, for it is seen to project, 

 carrying the cellulose envelope before it, so as to form a little 

 protuberance, and this sometimes attains a considerable length 

 before any separation of its cavity from that of the cell which gave 

 origin to it begins to take place. This separation is gradually 

 effected, however, by the infolding of the ectoplasm, just as in the 

 preceding case ; and thus the endochrome of the branch cell becomes 

 completely severed from that of the stock. The branch then begins 

 to elongate itself by the subdivision of its first-formed cell ; and this 

 process may be repeated for a time in all the cells of the filament, 

 though it usually conies to be restricted at last to the terminal cell. 

 The very elongated cells of some species of Confervacea? are 

 characterised by the possession of a large number of nuclei. They 

 are multiplied by zoospores, produced apparently indifferently from 

 any cell of a filament, by free-cell formation. These zoospores arc 

 of two kinds, larger or smaller ; the larger kind have either two or 

 four cilia, and germinate directly ; the smaller are biciliated, and 

 conjugation between them has been observed. 



Nearly allied to the Confervacere is a very interesting plant in 

 which a true sexual mode of reproduction has been observed. Sphaero- 

 plea annulina, the development and generation of which have been 

 specially studied by Dr. F. Cohn. 1 The oospore, which is the pro- 

 duct of the sexual process to be presently described, is filled when 

 mature with a red oil, and is enveloped by two membranes, of which 

 the outer one is furnished with stellate prolongations (fig. 431, No. 1 ). 

 When it begins to vegetate, its endochrome breaks up first into 

 two halves (No. 2), and then, by successive subdivisions, into numerous 

 segments (Nos. 3, 4), at the same time becoming green towards its 

 margin. These segments, set free by the rupture of their containing 

 envelope, escape in the form of motile zoospores, which are at first 

 rounded or oval, each having a semi-transparent beak whence proceed 

 two cilia; but they gradually elongate so as to become fusiform 

 (No. 5), at the same time changing their colour from red to green. 

 These move actively for a time, and then, losing their motile power, 

 begin to develop themselves into filaments. The first stage in this 

 development consists in the elongation of the cell, and the separation 

 of the endochrome of its two halves by the interposition of a vacuole 

 (No. 6), and in more advanced stages (Nos. 7, 8) a repetition of the 

 like interposition gives to the endochrome that annular arrange- 

 ment from which lhc plant derives its specific name. This is seen 

 at No. 9, a, as it present^ itself in the filaments of the adult plant ; 

 whilst, at ft. in the same figure. \\ e see a sort of frothy appearance 

 which the endochrome comes to possess through the multiplication 

 of the vacuoles. The next stage in the development of the filaments 

 that are to produce the oospheres consists in the aggregation of the 

 endochrome into definite masses (as seen .-it Xo. 10, a), which soon 

 become >t;ir-shapcd (as seen at &), each one being contained within a 

 distinct compartment of the cell. In a somewhat more advanced 

 stage (as >een at Xo. 11. ), the masses of endochrome begin to draw 

 1 Aim. des Sci. Nat. ll'ino sor., Bot., torn. v. 1856, p. 187. 



