Mr. HassalPs Notices of British Freshwater Conferva. 35 



nate disposition of spores and empty cells does not invariably 

 prevail, this will not affect the truth of the statement that 

 spores are sometimes formed without union of the filaments, 

 for that is incontestably proved by reference to the species of 

 Zygnemata spoken of above ; nor does it disprove the theory of 

 the formation of spores by the mingling of the contents of two 

 adjacent cells, the one of which is provided with fertilizing 

 matter, the other with that which is to be fertilized ; for in the 

 supposed instances of departure from the arrangement re- 

 ferred to, it might be fairly inferred that those spores not in 

 communication with an empty cell would not be fertile. It 

 must be borne in mind, likewise, that the material contained 

 in the spiral tubes previous to its passage from one cell to the 

 other, contracts itself into a little mass not usually of a regu- 

 lar form, but which might assume the appearance of a spore 

 without possessing the fertile properties of one. This must 

 be discriminated from the true spore. 



The formation of spores without union of the filaments is not 

 confined to these three species, but occasionally happens with 

 some other species of the genus, more especially with what is 

 to be regarded as a variety or condition of Zygnema porticale 

 (Z. quininum of Agardh). In this the same disposition of spores 

 and empty cells is remarked, but there is no direct channel 

 of communication between the cells, the coalition of the con- 

 tents of which being brought about by the rupture of the par- 

 titions which separate them, when these do not give way, the 

 cells swell up and assume a remarkable moniliform appearance 

 not peculiar to the species, but occurring in several others where 

 union is prevented by any cause. It is curious to notice also 

 that many of the cells throw out irregular and blind processes, 

 thus evincing a strong tendency towards union with the cells 

 of other filaments, which union would appear to have been 

 frustrated by the operation of some unexplained cause ; per- 

 haps the motion of the water in which the species was grow- 

 ing. 



In a species of Zygnema which I have named Z. polymorphism, 

 the spores are likewise formed in some of the filaments without 

 union, but somewhat differently from the manner in which this 

 is brought about in the species hitherto spoken of. In this there 

 is no alternate arrangement of spores and empty cells, a spore 

 being placed in every cell ; but these cells it is to be observed 

 are twice as long as those^which contain spores formed in the 

 usual way by the union of the cells of different filaments ; so 

 that each spore contained in these elongated cells is constituted 

 of the same quantity of material as the regularly formed spores, 

 but that the elongated cells at the period of the formation of 



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