190 Dr. G. C. Wallich on Desmidiacea from Lower Bengal. 



occurs with reference to the sporangial condition of Aptogonum 

 Baileyi : " Professor Bailey has sent me a drawing of the con- 

 jugated state, very interesting from its resemblance to a condi- 

 tion of Desmidium Swartzii, which I had doubtfully regarded as 

 the sporangia of that species. In both plants it is difficult to 

 understand the process or to distinguish the coupled filaments, 

 since the appearance is merely that of a much enlarged and torn 

 filament." 



It was my good fortune to meet with the sporangial condition 

 of both forms in considerable abundance, and thus to detect the 

 true mode in which the sporangial filament is produced. The 

 appearance of the mature sporangial filament is precisely similar 

 to that figured by Mr. Ralfs (tab. 4), and tallies with the general 

 description given in the paragraph last quoted. But during 

 the process of formation it has been found by me to be the joint 

 produce of two ordinary filaments. By what mysterious vital 

 tendency these ordinary filaments are drawn together, we shall 

 probably never learn. But that something more is necessary 

 than the mere accidental coming in contact of two filaments is 

 at once evident from the fact that, were nothing more needed, 

 filaments would be found at times held together, by a single pair 

 of conjugated cells, at right angles or inclined towards each 

 other. This is never the case. The filaments engaged are in- 

 variably placed parallel to each other, and although cells here 

 and there appear to be abortive, the entire number for which 

 there are pairs gradually become fused together. When a few 

 cells have united by this process, the remainder are possibly 

 placed in the most favourable position to take their share in it ; 

 but even this leaves much to be accounted for, and more espe- 

 cially the projection of the elongated sac-like vesicles in a direct 

 line towards each other, whilst a portion of each filament re- 

 mains separated from its fellow by a considerable interval. 



The process takes place in the following order. From the 

 base of one of the constrictions a minute sac is protruded. As 

 it extends in size, the adjacent lobes are pushed widely asunder, 

 the proximate angles become turgid, and the endochrome, which 

 has become condensed at this point, is gradually poured into 

 the sac. The already conjugated cells are kept asunder by their 

 enclosed sporangia, at a distance nearly equal to the diameter of 

 the filament. The elongated sacs at first simply impinge upon 

 each other. Shortly, however, they become incorporated, the 

 interposed portion of double cell-wall is absorbed, the contents 

 of the opposed joints coalesce, and form the large oblong or 

 circular sporangial bodies which we find occupying the enlarged 

 common cavities between the two conjugated filaments. Lastly, 

 the sporangia remain for a time encysted as just described ; but 



