14 NATURAL HISTORY SOCIETY OP DUBLIN. 



tibus, compositum." Now, such a diagnosis of the genus, while it does 

 not seem calculated to exclude all that it ought, appears to me to omit 

 an additional important character pervading all the species intended to 

 be included therein (if we except, as we ought, Palmoglcea Roemeriana, 

 Kiitz.), and that is the elongate or oblong form of the cells. As I 

 should be disposed to understand it, putting aside his Palmoglcea Roe- 

 meriana, Kiitzing must have established his genus Palmoglcea for the 

 reception of, and meant it to include, all those Palmellaceous Alga} 

 (except the one species forming his genus Trichodictyon, separated from 

 his Palmoglcea with little reason) possessing oblong, cylindrical, or 

 elliptic cells with granular contents, each cell possessing only a single 

 simple special mucous coat, not persistently included coat within coat, 

 the whole becoming confluent into an indeterminate gelatinous stratum 

 of greater or less density or tenuity. It is true that, of course, in the 

 specific characters and diagnosis of sub-groups, the elongate form of the 

 cells is alluded to, but I do not think a character so obviously generic 

 should have been left to be sought for amongst the specific. But the 

 fact of P. Roemeriana being included in the genus compelled him to 

 omit this character from the diagnosis. 



It is, indeed, with much diffidence that I venture to suggest that Kiit- 

 zing' s three subdivisions of his genus are founded upon wholly unreliable 

 distinctions. These distinctions in regard to the two principal subdivi- 

 sions, P. Roemeriana forming the third, are based, so. far indeed as I 

 can judge, merely on the comparative density or tenuity of the gela- 

 tinous " matrix ;" or, in other Avords, the supposed greater or less readi- 

 ness with which the special mucous investments of the cells remain in- 

 dividually defined, or become confluent with each other, thus rendering 

 the "loculi" (Kiitz.) more or less noticeable, or not at all perceptible. 

 These distinctions seem to be by no means of the constancy requisite for 

 usefully available characters ; indeed, as A. Braun*' 1 well observes, of so 

 little value are they as to render it doubtful in which section we are to 

 seek a particular species. This remark was made especially in regard 

 to a plant named by him, as most approaching to truth, Palmoglcea 

 macrococca (Kiitz.) ; but I venture to think that the plant meant by 

 A. Braun was not that so named by Kiitzing ; nor, indeed, probably 

 any described by that celebrated author. Indeed, the degree of moisture 

 of the situation in which these plants grow seems to exercise a consi- 

 derable influence on the consistence of the common gelatinous stratum. 

 A mass of one of these species in drying assumes a firmness and a some- 

 what elastic tenacity before shrivelling up. In those species which 

 grow wholly in water, the gelatine is of considerable tenuity, and the 

 cells sometimes even live free. 



But in this genus Palmoglcea it will seem evident, I think, upon a 

 careful examination of the living plants, that there are associated forms 

 of readily distinguishable diverse generic types, the most obvious com- 



" Rejuvenescence in Nature," translated for Ray Society, 1853, p. 327. 



