266 NATURAL HISTOKY SOCIETY OF DUBLIN. 



found presenting themselves in every specimen with absolutely unmis- 

 takeable clearness, that is, if unhealthy or deteriorated specimens should 

 again come under consideration — yet I believe a certain tout ensemble 

 will, even under such circumstances, readily satisfy the eye familiarized 

 with their appearance in their ordinary and healthy condition of their dis- 

 tinctness inter se. The plants adverted to under the names quoted by 

 Dr. Hicks, but adopting here the names which I regard as the correct 

 ones, are Cylindrocystis Brebksonii, Meneghini, and Cylindrocystis crassa, 

 de Bary. Dr. Hicks, indeed, says, as I have quoted, that " the exact 

 characters are by no means settled by any one of these observers." I may 

 venture to refer to my own previous efforts to describe their generic cha- 

 racters, and I can only appeal therefrom directly to the fresh specimens 

 themselves. . 



Dr. Hicks writes that — " The question, first of all, arises, how is a 

 single cell to be distinguished from another single cell ? What reliable 

 characters are to be fixed upon which can be considered as of generic 

 value?" If he propounds these questions as regards the old genus 

 Palmoglcea, or rather as regards the three genera already quoted, I 

 should have ventured to think that my previous paper was an answer 

 in anticipation. Though in a diffuse way indeed, I think the descrip- 

 tions there given may be found to contain the characters enabling an 

 observer to decide to which, if to any, of the three genera, Cylindro- 

 cystis, Mesotasnium, and Spirotcenia, a single cell belongs. Dr. Hicks 

 asks — " How can we tell whether it be a fixed form, a separate entity, 

 or merely a transitional form of some other growth ?" Again I venture 

 to reply, if this question be put as regards the forms immediately under 

 consideration, that I should be disposed to say (so far, I think, as our pre- 

 sent knowledge goes), that a sufficient answer is, that they each repro- 

 duce their like by a conj ugative act, thus renewing the species. For, 

 inasmuch as conjugation must be looked upon as a true generative act, 

 as I regard it, we must suppose that this takes place when the plant 

 has reached the end of its existence, ana has arrived at the ultimate 

 stage in its history — that is when it is at maturity — each of the conju- 

 gating pair of cells surrendering individual existence in giving origin, 

 by the union of their contents, to the spore from which is to be evolved 

 the primordial individuals of the next generation. 



And this leads to an important point in the argument, bearing on 

 the difference of opinion between Dr. Hicks and myself on the matter 

 immediately in question — I mean, the value or import to be attributed 

 to the conjugative act, as to which point I feel bound altogether to agree 

 with Professor de Bary.* 



Dr. Hicks considers it " merely an act of fusion" — that is certainly a 

 brief but true definition of the simple act in itself ; but it is not the modus 

 operandi of the mere act that is in dispute, but the physiological signifi- 



Untersuchungen uber die Familie der Conjugaten." 



