191 



On Certain Immature Forms of Diatomace.e. 



By G. C. Karop, M.E.C.S., &c. 



{Read August 27th, 1880.) 



I slioukl like the attention of Diatomists to be drawn at the present 

 season, when field excursions are being organised, towards the eluci- 

 dation of the true sexual generation in these plants. Whilst recently 

 examining the rootlets of some duckweed, I was much struck by 

 finding little groups of the tiniest diatom-like bodies, by far the 

 smallest specimens of such forms I had ever seen. Having no 

 means of measurement at hand, I should estimate them of the length 

 of -J- the width of a human blood- corpuscle — that is to say, if the 

 blood corpuscle were square, three average ones would just cover it. 

 They varied in size somewhat, and nearly all seemed in a healthy 

 condition, possessing clear yellow-brown endochrome. In their im- 

 mediate neighbourhood were some very small Goinphonema, usually 

 only two on a \/-shaped stipes, and one or two larger ones under- 

 going binary division. Altogether the whole group gave one the 

 idea of a family, but for the fact that the bodies composing the mass 

 of small frustules were distinctly navicular, and were lying flat on 

 the cells of the rootlet ; a very feAV only standing upright. On this 

 account, and from finding no mature purely navicular forms any- 

 where on the duckweed — although, bear in mind, my stock was 

 extremely small, being the washings of a bundle of watercress only — 

 I conjectured them to possibly be the pseudo-navicellas of some 

 Gregarine inhabiting Entomostraca ; so I got rid of the surplus 

 water with blotting-paper, and added strong nitric acid again and 

 again in the gentlest manner in small drops, sucking it up each 

 time with paper, until everything but the diatoms was destroyed, 

 the small bodies remaining intact ; this proving them to be inter- 

 penetrated with silex or other powerfully resisting matter. I need 

 scarcely say I could detect no markings which would have set the 

 question at rest, but I feel convinced they were a brood of young 

 JouRN. Q. M. C., No. 46. q 



