Reproduction & Multiplieation of Diatoms. By Count Gastraeane. 25 



selves too easily to be drawn on to generalizations without carefully 

 examining whether these generalizations will stand criticism, although 

 founded on well-ascertained particular facts. 



The same tendency has contributed to retard the progress of our 

 knowledge of the reproduction of diatoms, which is the principal 

 function of all living beings, but which, in respect to diatoms, has 

 been relegated to a secondary position subordinate to autofission, which 

 I can never regard as reproduction, but simply as an extension of the 

 life of the individual. As Dr. Pfitzer does not admit that the siliceous 

 cell of diatoms can increase in size ; and, recognizing at the same time, 

 as the consequence of autofission, the successive diminution of the 

 young frustules, when they have thus arrived at their minimum 

 dimensions, he ingeniously brings in at this point the intervention of 

 sexual conjugation, resulting in the production of an auxospore, the 

 purpose of which would be the formation of one or two sporanges. 

 According to Pfitzer these have the sole purpose of giving birth to 

 two sporangial frustules which repeat the typical form, but in larger 

 dimensions, with the object of again commencing another descending 

 series, until the ofispring are reduced to the minimum size. 



I feel compelled to say that this theory is ingenious, but not true. 

 I say that the theory is not true because, supported by the authority 

 of Prof. H. L. Smith and of Dr. Wallich, I regard the sporangial 

 frustule not as a normal, but rather as a monstrous form, which is 

 incapable of multiplying by deduplication, and is only destined for a 

 transitory purpose, that of the incubation of the sporules received 

 by it. This explains the fact that in the gatherings of Cymhella 

 (GoGconema) lanceolata Ehrb. there are a few large specimens of 

 uniform size, amongst a very large number of small ones of various 

 dimensions, but which cannot constitute a continuous series with 

 the former. In the same way, among Stauroneis gracilis Ehrb., 

 ;S^. Plioenicenteron is to be met with, which being, according to 

 Prof. H. L. Smith, nothing but the sporangial frustule of 8. gracilis, 

 has always, in the same gathering, a uniform size, larger than that of 

 this species, which, on the contrary, varies greatly in size. Similarly, 

 another argument against Dr. Pfitzer's theory, at least in the general 

 sense in which some apply it, is the fact that the sporanges, as often 

 happens with the lower forms of vegetable life, frequently reproduce 

 the species by means of gonidial sporules, without having recourse to 

 the formation of sporangial frustules or of anything equivalent to 

 them. Demonstration of this seems to me to be afforded by the 

 memorable observation of Thwaites reported in vol. ii. of Smith's 

 ' Synopsis,' on Plate A, drawn ad naturain by Tuffen West, where are 

 to be seen sporanges of Epithemia turgida Ktz. containing a number 

 of round corpuscles, perfectly definite and of uniform size, which it 

 seems to me impossible to interpret otherwise than as sporules. In 

 such a way it becomes easy to understand the formation of cysts 

 inclosing broods of diatoms which would be produced from these 

 sporules, while the sporange would increase in size and become the 



