800 Transactions. — Botany. 



growth to the production agam of another " zygospore." But, as he also 

 very truly observes, this would be practically impossible with the Desmi- 

 diesB, for the " zygospores " in very many instances are quite unknown, and 

 in all are difficult of detection. I may observe here that in the course of 

 three years study of these plants I have never met with a single instance of 

 a Desmid with attached zygospore. Scattered bodies, which appeared to be 

 zygospores, I have seen, but, as Ealfs remarks, unless they are actually 

 attached to segments of a frond it cannot be well known to what plant they 

 belong. Moreover, although zygospores have, by other observers, been fre- 

 quently seen, their ultimate history is in all cases at present obscure ; and 

 as the " Micrographic Dictionary " says, " the reproduction of the Desmi- 

 diaceffi still offers a wide field for investigation." Conjugation, in its earlier 

 stages, I have seen on a few occasions. 



On the other hand, the process of division seems to be much more fre- 

 quent, and I have myself observed it several times in the genera Closterium, 

 Micrasterias, Docidium, and others. In the filamentous genera, such as 

 Hyalotheca, division is less common. 



Now, although the actual following-out of the process of conjugation may 

 be difficult, or perhaps impossible, I take it that when on several occasions 

 the process of division is to be observed ; when, in such cases, the resulting 

 frond is identically similar to other and frequently seen fronds ; when there 

 is also at different times of the year, and perhaps in different years, com- 

 plete similarity in the specimens examined ; and when no trace can be 

 found, in descriptions of species by authors, of fronds having the same cha- 

 racters — there is at least very strong evidence that the plants under review 

 form a definite species different from the known species. To use Mr. 

 Archer's words, " Constantly recurring identical forms must be assumed to 

 be the descendants of similar progenitors."* Moreover, division, as I 

 imagine, can only take place in mature fronds ; immature plants could 

 scarcely propagate ; consequently any plant seen in process of division 

 must, if no previous record of its characters can be found, be taken as new. 

 For these reasons I have ventured to set down a few plants as new 

 species, and not merely as varieties. Eeferring again to the Diatomacese, I 

 believe that it has been ascertained that about ninety per cent, of those plants 

 in New Zealand belong to European species. In the Desmidieae, out of 

 sixty plants I consider six new, and two doubtful ; not a larger proportion. 

 As I have used the word " varieties," it may be weU to remark that in 

 many of the species which I have set down here as European, more espe- 

 cially perhaps in the genus Cosmarium, I have noticed peculiarities which do 



* Loc. cit., p. 238. 



