4 Mr. H.J. Carter on the Conjugation of 



small frustules is the restoration of the largest size of the spe- 

 cies ; but perhaps not the most important point. In what way 

 the small frustules are produced I am ignorant. Braun states 

 that the effect of cell-division in the Diatomese is to reduce the 

 size of the frustules *. This is evident enough in the cells of 

 the Spirogyr(2 ; and Meneghini has pointed out how it must be 

 the case from the conico-truncate form of Cocconeis, where the 

 plane of division is parallel to the base of the frustule f- But 

 Braun deduces his opinion from what occurs in Gloeocapsa, where 

 " the size of the cells diminishes with the increasing magnitude 

 of the family stock {phytodon%)/' that is to say, that the last ge- 

 nerations of cells are smallest. 



That quantity should be required for restoring the size of the 

 species, would appear from what takes place in the form of Spi- 

 rogyra already noticed, where the original cell, after having 

 been divided into four equal parts, ends in reuniting the con- 

 tents of each contiguous two of these to form two new spores. 

 Still more striking is the conjugation of two filaments of another 

 species, where the cells of one happen to be divided into only 

 two, and those of the other into four parts each. Here, although 

 the conjugation is commenced as usual by active tubulation, the 

 latter proves abortive; for the protoplasm of the large cells 

 soon withdraws itself from the tube, and wraps its contents up 

 into an elliptical spore of the normal size of the species ; while 

 the contents of every other small cell in the opposite filament 

 (the intervening ones not sporing at all) also wrap themselves 

 up into small globular spores respectively, but not without a 

 strong attempt at first to mix with those of their opposite neigh- 

 bour; — inasmuch as, in one instance, the tubulation of the 

 small cell with the large one appeared to have been entirely 

 formed by the former, whose contents had even passed a little 

 way into the latter, but finding the spore formed in the large 

 cell, were about to return to their own, or to remain where they 

 were when I saw them in this position. 



The rationale of this would at first appear to be, that the con- 

 tents of the large cell found themselves sufficient in quantity to 

 form the proper-sized spore, — which is the normal process in 

 Zygnema mirabile (Hass.) §, while those of the small cell in the 

 other filament found themselves in the opposite condition, and 

 after makiug an attempt to mix with their opposite neighbour 

 withdrew themselves, from finding no response, into their own 



* " Rejuvenescence in Nature." Eng. Trans., by A. Henfrey : Botan. and 

 Phys. Memoirs, published by the Ray Society, 1853. Foot-note, p. 132. 

 t Loc. cit. p. 406. X Loc. cit. Foot-note, p. 131. 



§ Hassall's British Freshwater Algae, p. 156. pi. 25. 



