286 PROCEEDINGS OF SECTION D. 



forms a zygospore, and a zygospore, too, of distinct characteristics 

 and fixed size. This is the necessary corollary of the idea that a 

 distinct outline infers a distinct species. As a matter of fact, how- 

 ever, every species includes among its multitudinous growing forms 

 quite a number of entirely distinct shapes — its type-forms or sub- 

 species. 



The question as to the formation of zygospores immediately 

 comes up for solution. We seem to have two possibilities to choose 

 between as a working hypothesis : — 1. That every sub-species has 

 a distinct zygospore, the zygospore answering to the outline. This 

 is simply the old idea, but now with an added difficulty, viz., that 

 as the species includes a number of sub-species, so it would also 

 include a number of different zygospores. There is also an original 

 difficulty about this idea, viz., the impossibility of conceiving, 

 several thousand distinct zygospores, to which may be added the 

 fact that only a few distinct types appear to be found in nature. 

 2. The second possibility is one zygospore for each species, distinct in 

 appearance when mature, but varying in size according to the 

 dimensions of the variation by which it is formed. The first of 

 these two will not, I think, commend itself to anyone, but the 

 second I desire to put forward as the true law of zygospores. It 

 means that Desmids forming the same kind of zygospore appertain 

 to the same species, however different in size and shape the cells 

 may he. In connection with the variation of the zygospore in size, 

 the case of Doc. trahecnla, cited above, may be mentioned. Both 

 Ehrenhergii and trabecula have smooth ellipsoid zygospores, vide 

 Ralp., T. xxvi, f. 4, for Ehrenhergii, and Wittrock, Om Gotl., p. 62, 

 where he gives the diameter as 125// for Doc. trahecnla. I have seen 

 a specimen of the former ; it was broadly oval and measured 66 x 

 48. Ralp. gives 90/^. 



Having lately had the opportunity of perusing W. & G. S. 

 West's Monograph of the British DesmUiiac.cB, I was specially 

 interested to note the support afforded to this rule by the figures of 

 zygospores. In Vol. I, PI. i, figs. 6, 7, 14, those of Gon. mono- 

 tcenium, Gon. Brehissonii, and Gon. Br eh. var. IcBve, are all exactly 

 ahke, but differ in size. These three Desmids are certainly forms 

 of one species. They are all quite common round Sydney. The 

 subcapitate head of Gon. Brehissonii unrolls as the cell swells 

 upwards from the middle — as in Docidium. (The same subcapitate 

 end I have observed lately in a young form of a species of Spiro- 

 tania ; its object appears to be to ensure a truncate apex.) Com- 

 pare also PI. vi. Pen. cylindrns and Pen. ciiticulare. Still more 

 noticeable are the zygospores of Eit. ohlongum, Eu. didelta, and Eu. 

 ampullaceum in Vol. ii, PI. xxxv, figs. 2, 7, 10. I have no knowledge, 

 unfortunately, of these three Enstra, none of which occur here as 

 far as I know, but there is nothing whatever to prevent them all 

 being forms of a single species, however they may differ in outline. 

 Nor is there any fundamental difference in their outUnes. Compare 

 the shape of the polar lobe in ampullaceum, affine, crassum, 

 ohlongum ; these and many others have all practically the same 



