AJKCHEK — ON PALMOGLCEA MACROCOCCA (KUTZ.) 21 



Such, as briefly as I can convey it, is some account of the genus 

 Mesotamium (Sag.), the last of the genera into which Palmoglcea (Kiitz.) 

 seems capable of being divided. Undoubtedly the three principal, and 

 those most nearly related to each other, are Spirotaenia, Cylindrocystis, 

 and Mesotaenium — the two others above alluded to should, so far as I 

 can judge, have never found a place in Palmoglcea. Of these three, 

 Spirotsenia may, I think, be said (as far at least as regards the forms 

 themselves) to bear a relationship to Spirogyra similar to that which 

 Cylindrocystis bears to Zygnema, and possibly Mesotaenium may be con- 

 sidered to possess, in a great measure, a relatively similar relationship 

 to Mesocarpus or to Leptocystinema (mihi). 



The query with which I commenced this paper suggested itself to 

 me after having searched for and having tried to examine our Dublin 

 forms included in Kiitzing's genus, and upon a re-perusal of Alex. 

 Eraun's remarks,* where that author observes that " the species of the 

 genus Palmogloea, as established by Kiitzing, cannot be certainly deter- 

 mined either by the characters given in ' Species Algarum,' or by the 

 figures given in 'Tab. Phyc' " And he goes on to say, that in the 

 species represented by himself, which, doubtfully, he calls P. macrococca, 

 "the jelly-like envelopes are sometimes distinguishable singly, some- 

 times not, which renders doubtful even the section in which we are to 

 seek the species;" and he afterwards expresses an opinion that several 

 of the species (citing six) will have to be combined as forms of one and 

 the same species. With that writer I must concur in admitting the 

 difficulty of identifying Kiitzing's forms, as well as even the uncertainty, 

 as I before indicated, in deciding the section in which we are to seek a 

 particular species. But I think it must be admitted that, seizing upon 

 other distinctions than those put forward by Kutzing, abundantly dis- 

 tinguishable forms, even generically separated, here present themselves, 

 as I have endeavoured to show. It may indeed be quite probable that 

 some of his forms are described as distinct upon characters too trivial ; 

 thus I dould be disposed to suggest, altogether conjecturally, that his 

 P. vesiculosa and P. macrococca may be possibly identical — P. lurida 

 and P. rupestris. — P . protuberans and P. micrococca ; but in the main, 

 so far as I can judge, the forms generally referred by him to this genus 

 seem to be distinct. On the other hand, I fancy that, as might be ex- 

 pected, a few forms appertaining to Mesotaenium, described by Nageli 

 and De Bary, do not occur at all in " Species Algarum." 



In thus expressing an opinion as to the actuality and distinctness of 

 these species, which I would wish to do very far from dogmatically, I 

 am not unmindful of the statements made by writers as to the diamor- 

 phosis of these forms — that is, as to their being merely more or less 

 transitory conditions of higher plants. But it. indeed, appears to mo 

 that anything as yet adduced in support of the transition of a true 

 Palmoglcea — that is to say, of either a true Spirotaenia, Cylindrocystis, 



Op. cit., p. o27. 



