CASTRACANEj ON DIATOMACEiE. 257 



those of Thwaites, Griffith, and Carter. According to 

 these observers, cases of conjugation have been noticed in the 

 Diatomacecs similar to that which occurs in the Desmidiece, 

 and this in thirty-one distinct species belonging to seventeen 

 genera ; and from which conjugation resulted the formation 

 of one or two sporangia, and of one or two sporangial frus- 

 tules. 



According to Mr. Smith, the various conditions which 

 accompany the state of conjugation may be ranged in four 

 classes — 1. From the two conjugate frustules are produced two 

 sporangia, as in the genera Epithemia, Cocconema, Encyonema, 

 and Colletonema. 2. From the conjugation of two frustules 

 arises a single sporangium, as is witnessed in Hhnantidiuni. 

 3. The two valves of a single frustule separate, the contents 

 increase rapidly in volume, and finally become condensed 

 into a single sporangium, as has been observed in Coccotieis, 

 Cyclotella, Melosira, Orthosira, and Schizonema. 4. Lastly, 

 from the two valves of a single frustule as above, results, by 

 a process of conjugation, the formation of two sporangia, as in 

 the genera Achnanthes and Rhabdonema. 



The formation of one or of two sporangia, the result of the 

 process of conjugation, can only be regarded as a reproduc- 

 tion of the species by germs, which is the most ordinary 

 mode by which plants are propagated, the sporangium in 

 the present case being considered as the organ destined to 

 elaborate and emit the fecundated germs. But all this is at 

 the present time involved in such obscurity that the author 

 of the ' Synopsis of British Diatomacete ' merely observes 

 that it " seems to him " that the result of the sporangium 

 may be the production of a sAvarm of diatoms. 



Nor does Dr. Carpenter, in his valuable work, ' The Micro- 

 scope and its Revelations,' appear to be more explicit on this 

 point, saying only that he is inclined to believe in the multi- 

 plication of the Diatomaceae by the subdivision of the endo- 

 chrome in the gonidia, from which they emerge either in the 

 active condition of zoospores or in the state of hypnospores. 

 For this doubtful observation he relies upon the authority of 

 Focke, who, in relating certain observations relative to the 

 multiplication by germs, makes use of tlie argument from 

 anulogy with what takes place in other protophytes, which, 

 besides possessing the faculty of organic multiplication by 

 fission of the cell, are also capable of being formed by the 

 ordinary method proper to all organisms, both vegetable 

 and animal, in Avhich reproduction is effected by sexual con- 

 junction. 



Moreover, various observations have already been recorded. 



