18 NATURAL HISTORY SOCIETY OF DUBLIN. 



terlaced in a loosely reticulated manner, so as to leave wide roundish in- 

 terspaces, in which occur the large ovato-elliptic cells, either singly or 

 in one, two, or more pairs, surrounded hy their broad and copious finally 

 confluent gelatinous coatings. These filaments do not seem to differ 

 from those frequently growing along with other Palmoglcean and other 

 Palmellacean forms, nor do they seem organically connected with, or 

 in any way belonging to the plant in question. Similar filaments are 

 by Kiitzing himself referred to Leptothrix, or perhaps to Hypheothrix. 

 In fact, it would here seem as if it were only because these filaments 

 often occur along with this plant in great quantity, penetrating through 

 the mass, and because the cells themselves, during active vegetation, 

 increase vigorously from numerous centres, and copiously giving rise to 

 their gelatinous investments (this taking place pretty equably over the 

 mass), that the filaments are forced to give room, and become obliged to 

 assume more or less of a reticulated disposition. But that these filaments 

 possess no importance, nor any organic relationship, so far as I can see, 

 as regards the plant in question, is, I think, proved by it being met 

 with, as I have often found it (always supposing that I am right in my 

 identification of the species, of which, indeed, I have myself no doubt) 

 unaccompanied by filaments, or these so sparing as to render Kiitzing' s 

 description of the plant as inappropriate as, so far as I can see the in- 

 troduction of these filaments into the generic character at all is erro- 

 neous. In regard to his Cylindrocystis crassa, De Bary omits any 

 notice of such filaments altogether ; yet, as I before indicated, I believe 

 these plants are identical. 



But, in order to explain the occasionally occurring peculiarity alluded 

 to, in the mode of growth or self-division of the cells themselves in this 

 plant, dwelt on by De Bary, I shall momentarily draw attention to that 

 which prevails in the entire of its allies, and then advert to the varia- 

 tion sometimes met with in this species itself. 



In the related species of Penium, Spirotaenia, Cylindrocystis, and 

 Mesotsenium (as well as those elongate, but apparently not at all related 

 forms included in Glceothece (Nag.), Stichococcus (Nag.), &c. &c), the 

 direction of self-division occurs always in a line at the middle, at right 

 angles with the original longitudinal axis of the mother-cell. Now, in 

 Cylindrocystis Brelissonii, along with the elongation of a cell, prepa- 

 ratory to self-division, a longitudinal extension, and a transverse sub- 

 division of the central corpuscles belonging to each of its halves takes 

 place, thus causing the now two corpuscles of each half to lie in the di- 

 rection of, and on a line with, the longitudinal axis of the original 

 mother-cell. Presently ensues a segmentation and division into two of 

 the cell itself at the middle, in the transverse direction, and, as stated, 

 in a line at right angles to the longitudinal axis, the original nucleus 

 vanishing, and a new one for each half, that is, each daughter-cell, 

 making its appearance, according to De Bary. In C. crassa (De Bary) 

 = Trichodictyon rupestre (Kiitz.), previous to division of the cell itself, 

 there is no subdivision of the central corpuscle of each half, but on the 

 formation of a septum it seems to ensue. Its subdivision may take place 



