DUBLIN NATUKAL HISTOBT SOCIETY. 37 



Such, then, is an account, deficient, as I regret it is, in many points, 

 of what I cannot but look upon, so far as I can make out, as a new and 

 unrecorded phase in the life-history of this beautiful and interesting fa- 

 mily, theDesmidiaceae, — a life-history, still obscure in many of its details, 

 but yet one which I aver will not yield in interest to any other portion in 

 the wide domain of our comprehensive science of I^atural History, and one 

 also on which I shall deem myself very fortunate and very happy should 

 these humble observations of mine, here recorded, ever be found even- 

 tually to shed even a dim and solitary ray of light in its elucidation. 



Mr. William Aecheh also read a paper — 



FTJETHEE, NOTES ON ABNORMAL GROWTH IN THE DESMIDIACE^. 



In a former paper read to this Society {vide IS'at. Hist. Eev., vol. vi., 

 page 469), I drew attention to an abnormal mode of growth affecting 

 several species of Desmidiacese. This consisted in there being produced 

 between the old segments, not a pair of new ones eventually to become 

 symmetrical with the old, but an irregular, more or less unsymmetrical 

 inflated expansion, forming with the old segments but one uninterrupted 

 cavity ; and this kind of monstrosity I endeavoured to show might pro- 

 bably be primarily due to the omission of the formation of a septum as 

 a preliminary to ordinary vegetative growth. In PL xiii., Fig. 7, I bring 

 forward what seems to be a further extension of the same identical con- 

 dition oi Arthrodesnms incus, as that figured in PL xxxiii.. Pig. 11, 

 I. c. In the case last indicated, as in the others, there must exist a 

 suture between the older segments and the intermediate abnormal growth 

 — that is, the latter has become interposed between the older segments 

 by their separation at the original suture. 



]S"ow Pig. 7 of the present plate seems to indicate that the vegeta- 

 tive energy is not necessarily arrested ; for between the central growth 

 (of the /rs^ case in A. incus figured), and each of the original segments, 

 a new expansion has been formed — the whole, that is, the older seg- 

 ments and the now three intervening portions (the middle one being the 

 older) forming still one uninterrupted cavity, and filled with endo- 

 -chrome throughout. The entire structure, under a low power, might 

 be mistaken for a Scenodesmus ; but, when sufficiently magnified, its real 

 nature is quite apparent. The specimen (Pig. 7) occurred amongst 

 several others in the condition figured with my former paper (Pig. 11), 

 both mixed with multitudes in the normal state, some in the dividing- 

 condition. There does not seem any readily assignable limit to the 

 extent to Avhichthis monstrosity might be carried ; yet, even supposing it 

 had attained some considerable length, and that the extraordinary struc- 

 ture should survive its own fragility, a time must come, I conceive, as 

 in ordinary individuals, when its vegetative energy would be spent. 



Pig. 6 represents a remarkable mycelioid growth occun-ing within 

 a Closterium lunula, noticed in the paper alluded to, read to the Society 

 (page 472, I. c), remarkable on account of the impossibility', except on 



I 



