24 Transactions of the Society. 



Congress, to which I presented a note with the title, " The Theory of 

 the Keproduction of Diatoms," and which appeared in the Proceedings 

 of that Congress. In this memoir I adduced many arguments and 

 proofs to demonstrate the power of increase and extension of the 

 siliceous walls of living diatoms; but I do not think it will be 

 necessary to reproduce more than one of the many proofs adduced. 

 In vol. ii. of Smith's ' Synopsis,' plate lii. fig. 335, are represented 

 several sporangial frustules of Orthosira Dichiei Thw., of which 

 the equatorial diameter is increased by one-third, while the polar 

 diameter has, in elongating, occupied the cavity of several adjacent 

 cells, expanding its base, forcing its surface of contact to become 

 folded on itself, and dilating in proportion. No one will accuse 

 these figures of inexactness or exaggeration, since they were drawn 

 by Tuffen West to illustrate the classical work of W. Smith. 

 Having, moreover, the first century of the ' Diatomacearum species 

 typicae' of Dr. Th. Eulenstein, I have been able to compare the 

 above-named figure with the preparation of the same species, and 

 found them to agree perfectly. This observation confirms what was 

 long ago established by von Mohl, that the cytoderm of diatoms is 

 not a solid wall, but rather an organic membrane impregnated with 

 silica, and therefore that, as long as it remains under the influence of 

 life, it will be in a condition capable of increase and expansion. Dr. 

 Pfitzer, in denying this power to the walls of diatoms, when the 

 progeny has reached the minimum size, invokes the intervention of 

 the process of conjugation, which is not multiplication, but rather true 

 reproduction, and of which we shall speak directly. 



The process of autofission is cherished especially by botanists, 

 for it is what usually takes place among unicellular algae, to which 

 class diatoms belong, and has been actually observed in a great 

 number of cases among them. When fission takes place in a diatom, 

 it is the general opinion that, of the two valves formed in the centre of 

 the mother- cell, each is the exact counterpart of the valve which faces 

 it, on which it is stereotyped, reproducing it in its form and in its 

 minutest details. From this, as it seems to me, follows the impos- 

 sibility of autofission in (1) those genera in which the valves are not 

 exactly alike, as Cocconeis and Achnanthes ; (2) those in which the 

 two valves, although alike, yet in uniting, cross the axes of the figure, 

 such as Campylodiscus ; (3) those with similar valves, but arranged 

 in such a way that the homologous parts alternate, as Asterolampra 

 and Asteromphalus. It may be noted that, as far as has at the present 

 time been brought under my notice, none of the numerous cases of 

 fission that have been observed among diatoms controvert my view. 

 Hence I feel myself authorized to say that if the multiplication of 

 diatoms takes place actually by autofission, this fission can take place 

 only in certain genera, and that therefore it must be regarded rather 

 as the exception than as the rule. This is worth making known; 

 since not unfrequently naturalists of good repute, when treating of 

 organisms imperfectly known or but recently discovered, allow them- 



