ABCHEB — ox "palmoglceajs" alg^e. 271 



midiacese, but also conditions more complex are met with in various 

 species, to enter into detail here as to which would, however, be super- 

 fluous. Many of the zygospores become, as is well known, furnished 

 with variously fashioned spine and processes, which circumstance seems 

 to me probably to find a parallel in the less developed ones of CEdogo- 

 nium echinospermum. As is well known, very varied conditions are to 

 be met with appertaining to, and characteristic of, various species. Thus 

 the spinous or non-spinous zygospores — the simple or variously branched 

 spines — the orbicular, or quadrate, or characteristically lobed figure of 

 the zygospore — the relative positions of the conjugating pairs of indivi- 

 duals — the, so to say, double spore of Closterium lineatum — the con- 

 jugation following immediately on self-division in Closterium Ehrenber- 

 gii, C. Pritchardianum — the complete and persistent fusion of the parent 

 membrane in Hyalotheca dissiliens, Closterium parvulum — the remote 

 outer coat of the spore of Tetmemorus Icevis, &c, besides minor specialities 

 of detail proper to the various forms — all these can hardly be considered 

 as the accompaniments of an accidental phenomenon, in itself meaning 

 nothing, and destitute of significancy. 



But, in pursuing onward our examination of the conjugative process 

 and its results, the behaviour in Didi/moprium Grevillii, in which spe- 

 cies, of two conjugating filaments, the cells of one are always the re- 

 ceiving — those of the other the giving — cells in the conjugative act, leads 

 us to Spirogyra, in which these conditions are constant. In this latter 

 genus the receiving cell frequently assumes an enlarged and different 

 figure, often preparatory to, and in anticipation of, the accession of the 

 contents of the giving cell, thus, I think, exhibiting a certain significant 

 amount of differentiation. 



In Spirogyra and Zygnema, as is well known, the act of germina- 

 tion consists in the inner coat of the zygospore expanding and bursting 

 off the outer, and, while extending in length, becoming transversely 

 divided by a septum, the lower cell remaining always undivided as a 

 " root-cell," the upper becoming the first ordinary joint of the new plant, 

 thus differing from Cylindrocystis and Mesotaenium. But in this cha- 

 racteristic we have an analogy in Vaucheria, whose fertilized oospore does 

 not develope daughter-cells, each to give origin to so many new indivi- 

 duals, but grows at once into a single new plant, unicellular, of course, 

 like its parent. 



But, notwithstanding all these so varied, more or less complex con- 

 ditions, it may perhaps be still urged that, after all, such conjuga- 

 tion is but the union of the contents of two morphologically equiva- 

 lent cells. 



To this objection the conditions in the genus Sirogonium seem to 

 afford a valid answer. 



Two ordinary joints of a filament in Sirogonium mutually send out 

 short processes, as in Spirogyra, which become united ; thereupon there 

 ensues the formation of a septum (similarly to that of the vegetative 

 cell) in each of these united cells. In one, this septum, however, unlike 



