MICROSCOPIC FORMS OF VEGETABLE LIFE. 255- 



under a very interesting form in a plant termed Sphcsroplea annulina,. 

 the development and generation of which have been specially studied by 

 Dr. F. Cohn. 1 The 'oospore/ which is the product of the sexual pro- 

 cess 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 witk 

 stellate prolongations (Plate x., fig. 1). When it begins to vegetate, its 

 endochrome breaks up first into two halves (fig. 2), and then by succes- 

 sive 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 whence- 

 proceed two flagella, but which gradually elongate so as to become fusi- 

 form (fig. 5), at the same time changing their color 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 (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 #, 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 oospores, con- 

 sists in the aggregation of the endochrome into definite masses (as seen 

 at fig. 10, a), which soon become star-shaped (as seen at #), each one 

 being contained within a distinct compartment of the cell. In a some- 

 what more advanced stage (fig. 11, a), the masses of endochrome begin 

 to draw themselves together again; and they soon assume a globular or 

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

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

 ' antherozoids ' 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 the lower part 

 of fig. 12. These undergo further changes whilst still contained within 

 their tubular parent-cells; their color passing from green to red, and a. 

 second investment being formed within the first, which extends itself 

 into stellate prolongations, as seen in fig. 13; so that, when set free, they 

 precisely resemble the" mature oospores which we have taken as the 

 starting-point in this curious history. Certain of the filaments (fig. 14), 

 instead of giving origin to spores, have their annular collections of endo- 

 chrome converted into * antherozoids,' which, as soon as they have disen- 

 gaged themselves from the mucilaginous sheath that envelops them, 

 move about rapidly in the cavity of their containing cell (a, b) around 

 the large vacuoles which occupy its interior; and then make their escape 

 through apertures (c, c?) which form themselves in its wall, to find their 

 way through similar apertures into the interior of the spore-bearing cells, 

 as already described. These antherozoids are shown in fig. 15, as they 

 appear when swimming actively through the water by means of the two 

 flagella which each possesses. The peculiar interest of this history con- 

 sists in the entire absence of any special organs for the Generative process, 



1 "Ann. des Sci. Nat.," 4eme Ser., Botan., Tom. v., p. 187. 



