ARCHER ON PALMOGLCEA MACROCOCCA (kUTZ.). 27 



divided ; its inner ends bluntly rounded. Pig. 6, the cell divided. 

 Fig. 7, two cells about to conjugate. Fig. 8, two sucb cells in contact, 

 the parent coats slipping off. Figs. 9 to 13, various degrees of ad- 

 vancement of conjugation. Fig. 14, zygospore formed, with mucous 

 investment. Figs. 15 to 19, various mature zygospores. 



Now, as regards the position of the genus to which this plant belongs, 

 inasmuch as the mode in which the reproductive process is carried out 

 in any organism is always — and doubtless rightly — regarded as of more 

 importance than vegetative structure in deciding affinity, the fact that 

 in these forms reproduction is by conjugation most strongly points to a 

 close relationship with the Desmidiaceae and with the Zygnemaceae ; and 

 in this genus the process is essentially that which characterizes those 

 families. On the other hand, the gelatinous nature indicates considera- 

 ble affinity with the Palmellaceae ; but, with the exception of Palmo- 

 glcea, I am not aware of conjugation having been found in any other 

 genus of that family, though zoospores occur in some, while in regard to 

 others Professor Kutzing's* and Dr. Hicks' interesting observations 

 render their truly autonomous character doubtful, although I fancy each 

 has been perhaps too hasty and too comprehensive in his generalizations. 



Clearly this genus and Cylindrocystis are very closely related, and to 

 whatever group one belongs so does the other. By Nageli the genus 

 Mesotaenium is placed with the Desmidiaceae, and by De Bary both 

 those genera are classed in that family. By the latter writer the Con- 

 jugates are divided into three families — Mesocarpeae, Zygnemeae, and 

 Desmidieae — their distinctions drawn from the mode as to special details 

 of the formation of the zygospore and of the development of the young 

 plants originating therefrom, distinctions I need not more than allude to 

 here. The distinctions based upon the fact as to whether all the daughter- 

 cells originating from the germ-cell are again capable of self-division, or 

 whether one of the daughter-cells remains as a "root-cell" incapable 

 of further self-division — the former characterizing the Desmidieae, the 

 latter the Zygnemaceae — De Bary considers the only decided pervading 

 features absolutely separating these two families. Mesocarpeae are dis- 

 tinguished from both by peculiarities in the formation of the zygospore 

 itself. Suffice it that the genera in question, as indicated by that author's 

 original researches, in the mode of development, seem to accord with the 

 characters in that regard as specially appertaining to the Desmidiaceae. 



There is a character, however, which seems to pervade the family 

 Desmidiaceae, and is certainly demonstrable in every undoubted member 

 of the group. I allude to the well-known fact that the vegetative in- 

 crease of a cell, or " frond," is effected by the formation of two new 

 half cells, which become interposed between the older, so that the two 

 newly-produced cells consist each of a new and old half cell. Of course 



* Kutzing's " Die Umwandlung niederer Algenformen in hohere," &c, published 

 in " Natuurkundige Verhandelingen van de hollandsche Maatschappij der Wetenschappen 

 te Haarlem :" 1841. 



