CHR0N1200SP0RES OP HYDRODICTYON. 109 



all the phenomena of development. These modifications are 

 accompanied frequently by a secretion which commences in 

 the neighbourhood of the septa^ dividing the filaments of 

 Ulothrix, on the outer surface of which its products are depo- 

 sited. These filaments then acquire a very singular aspect ; 

 they become more manifestly pointed, and from being cylin- 

 drical, assume rather a moniliform appearance. At last, 

 their joints, considerably enlarged, separate one from the other 

 as so many distinct spores, but still always closely enclosed 

 by the proper membrane of their respective parent-cells. 



Similar phenomena are observed in the formation of the 

 hypuospores of Stigiodonium, Choetophora, and Draparnaldia, 

 which are all branching algee. In them also it is the ordinary 

 plant-cells which are transformed into sporiferous utricles. 

 It is further to be observed that the structure of the stem 

 in these algse, differs from that of the lateral branches, and 

 that the production of the hypuospores appears to concern 

 the cells of these branches, and to have nothing to do with 

 those of the stem. In Draparnaldia, the Chcetophora, the 

 two genera in Avhich the greatest dissimilarity exists between 

 the stem and the branches, the unmodified basillary cell of 

 the latter is not unfrequently seen supporting a string of 

 sporiferous utricles. 



The modifications that the generative cells of the spores 

 undergo, vary in the diflPerent species of the genera of which 

 we are speaking, and the uneven appearance of the fertile 

 branches is owing to them. Other differences arise from the 

 variable member of spores that each mother-cell can produce. 

 In Draparnaldia glomerata, the spores are produced some- 

 times isolated, sometimes binary or quaternary, and this 

 unequal fecundity of the fertile utricles is observed not only 

 in the different branches of the same individual, but also in 

 the various joints of the same branch. The parent-cells have 

 also two modes of existence. Some become moderately elon- 

 gated, and grow pari passu with the single spore that they 

 enclose ; they never open, and this spore never escapes from 

 their interior. The branches, in this case, assume in all 

 respects the aspect of the fertile filaments in Ulothrix ; they 

 become thick, brown, moniliform, and preserve for a long 

 time their first arrangement on the unaltered stem ; at length 

 they break up irregularly, and their disconnected elements are 

 dispersed. The spore, like that of Ulothrix, remains com- 

 pletely enveloped in the membrane of the mother-cell. 

 According to my own observations, this is always the case 

 where a single spore is produced in the conceptacle. 



In other parent cells in the same Draparnaldia glomerata j 



