GROWTH, ETC., IN THE DESMIDIACE.^. 287 



sideline from base to apex, a three-Iobed one ; their dimensions 

 are the same, too. Once frankly recognise that they may be growing 

 forms and the fundamental likeness appears at once. Note also 

 Monog., Vol. Ill, Cos. ornattim, PI. 78, f. 1-10 ; Cos. commissurale, 

 f. 11-14 ; and Cos. corbula, PI. 82. f. 9-11. These are forms of one 

 species ; the zygospores are identical. Compare the remarks by 

 J. A. Cushman.^ 



Zygospores are rare in this country, and I would like to broach 

 three ideas which may be proved or disproved by more fortunately 

 situated observers : — 



1. That the large strong-growing Desmids do not produce 

 zygospores, conjugation being the outcome not of strength but of 

 weakness. 



2. That the fully- developed cells of any species do not form 

 zygospores, and that cells found in conjugation are by that very 

 fact shown to be more or less degenerate. The zygospore I consider 

 to be an arrangement for keeping up the size of the species, hke the 

 auxospore of the diatoms — a confession of weakness. For fully- 

 developed cells to unite for this purpose could only tend to increase 

 the size. I have not seen many examples of cells in conjugation, 

 but in every case where I have seen them the cells were certainly 

 degenerate. Compare W. & G. S. West, "New Brit. Frw. Algce,'"^ 

 where an interesting array of zygospores is figured. The authors 

 themselves refer to the fact that in several cases the zygospores 

 had been formed by cells newly divided and not yet fully formed, 

 vide PL iii, f. 29, PI. iv, f. 43, and the note on CI. Ehrenbergii, p. 

 151. In three other cases than those cited, to my certain know- 

 ledge, the cells are degenerate forms, viz., Cos. pseudoprokiberans, 

 PI. iv, f. 34, St. margaritaceiini, PI. iv, f. 36, and St. orbiadare, 

 PI. iii, f. 28. None of these desmids are mature forms of the species 

 they represent. 



3. That every variation of a Desmid can form a zygospore, 

 even those which are exceedingly degenerate in size : cf. Cos. 

 tincium, Ralp.^ 



Again the zygospores themselves go through a course of 

 development. All are quite smooth at first, next papillae may 

 form which develope a spine at the apex, or simple spines may 

 develope directly from the body. All these spines are simple to 

 start with, but most become at least bifid with growth, and some 

 even twice or thrice dichotomus, with elegantly curled tips. 

 Compare Cos. orthopunctiilatmn, Schm. Zygo (I.e., 1907, PI. v, fig. 

 28), where a is the immature and b the more mature form ; also 

 Ralfs, T. vii, where spines may be seen in all stages on the same 

 zygospore. There are two different ways, however, in which this 

 fission comes about. In some zygospores {Cos. subspeciosum |y8 

 validius, Nord., for instance) the spines are first subulate but 



1 Bull. Torrey Bot. Club, Vol. 32, No. 4, 1905, p. 22.3. 

 ZJourii. Roy. Micros. Soc, 1896, part. 2. 

 3 Brit. Desm., PI. 32, f. 7. 



