332 confervacejE : — generation in spieeroplea. 



whereby the two parts of the filament are prevented from being 

 altogether separated. Sometimes the zoospore does not completely 

 extricate itself from the parent-cell ; and it may begin to grow in 

 this situation, the root-like processes which it puts-forth being 

 extended into the cavity. 



250. A true Sexual Generation has been observed in several 

 Confervacese, and is probably universal throughout the group. It 

 is presented under a very interesting form in a plant termed 

 Sphceroplea annulina, the development and generation of which 

 have been specially studied by Dr. F. Cohn.* The 'Oo-spore,' 

 which is the produce 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 pro- 

 longations (Plate xi. fig. 1). When it begins to vegetate, its 

 Endochrome breaks up — first into two halves (fig. 2), and then by 

 successive subdivisions into numerous segments (figs. 3, 4), at the 

 same time becoming green towards its margin. These segments, 

 set-free by the rupture of their containing envelope, escape as 

 Micro-gonidia, which are at first rounded or oval, each having a 

 semi-transparent beak from which proceed two vibratile filaments, 

 but which gradually elongate so as to become fusiform (fig. 5), at 

 the same time changing their colour from red to green. These 

 move actively for a time like the Zoospores of other Protophytes, 

 and then, losing their motile power, begin to develope them- 

 selves into filaments. The first stage in this development con- 

 sists in the elongation of the cell, and the separation of the endo- 

 chrome of its two halves by the interposition of a vacuole (fig. 6) ; 

 and in more advanced stages (figs. 7, 8) a repetition of the like 

 interposition gives to the endochrome that annular arrangement 

 from which the plant derives its specific name. This is seen at a, 

 fig. 9, as it presents itself in the filaments of the adult plant ; whilst 

 at b, in the same figure, we 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 Spores, consists in the aggregation of the Endo- 

 chrome into definite masses (as seen at fig. 10, a), which soon be- 

 come star-shaped (as seen at b), each one being contained within a 

 distinct compartment of the cell. In a somewhat more advanced 

 stage (fig. 11, o) the masses of endochrome begin to draw them- 

 selves together again ; and they soon assume a globular or ovoidal 

 shape (6), whilst at the same time definite openings (c) are formed 

 in their containing cell- wall. Through these openings the Antbe- 

 rozoids developed within other filaments gain admission, as shown 

 at d, fig. 12 ; and they seem to dissolve away (as it were) upon 

 the surface of the before- mentioned masses, which soon afterwards 

 become invested with a firm membranous envelope, as shown in 



* "Aim. des Sci. Nat." 4i£me Ser., Botan., Tom. v. p. 187. 



