OF THE DIATOME.E. 95 



from each other by any structural characters, seem to be j^hysiohgicaUi/ sepa- 

 rable by the mode in which they perform those actions wherein their life most 

 essentially consists." 



The process of conjngation has been used as an argument for the vegetable 

 natiu-e of Diatomeae by Mr. Thwaites and others. This subsequently seemed 

 to be set aside by the observation of apparent conjugation in Act'mophrys and 

 Oregarina observed by Kolliker and Cohn. However, this phenomenon 

 appears again in the ascendant as a vegetable characteristic ; for the observa- 

 tions of Mr. Weston {J. M. S. 1856, 122), of Leuckart, Lieberkuhn, and 

 others, go to show that the act believed to be one of conjugation in the 

 Actinoj)Jiri/s, is not really a process of reproduction, but merely a temporary 

 cohesion : moreover Lieberkuhn (Mem. de VAmd. Roy. Belgique, vol. xvi.) 

 proves that the production of the Navkellce is not necessarily a consequence 

 of the act of conjugation in the Gregarince. 



If futm-e research substantiate the fact that conjugation is essentially a 

 vegetable process, then the nature of the Diatomeos will no longer be doubtful. 



On a review of the arguments ui^ged on each side, and on consideration of 

 the whole structural and vital peculiarities of the Diatomese, we are disposed 

 to consider them of a vegetable nature — members of the great family of 

 Algse, and, together with many other unicellular plants, to constitute a group 

 known by the name of Protophyta. Nageli, in 1849, took this view, and 

 reckoned the Diatomeae as one of his eight orders of unicellular Algse, of 

 which the Desmidiaceos and Palmellaceae were other two. How close must 

 be the affinity of the Diatomese with the Desmidieas is shown by the fact of 

 the two families ha\ing so long been treated of together under the common 

 head and name of Bacillaria. And although sufficiently decisive characters 

 separate the one set of beings from the other, yet, in the grand phenomena 

 of hfe and organization, a true homology exists. The difference between some 

 Desmidiese and Palmellese is as much pronounced as it is between the former 

 and some Diatomea) ; and between these several orders, together with the 

 Zygnematse, various intermediate forms are to be found, which serve as con- 

 necting links. Although Mr. Ralfs would not now insist upon the distinc- 

 tions between the Desmidieae and Diatomeae, formerly laid down by him as 

 decisive, yet they may be here reproduced with advantage. 1. In Diatomeae 

 (op. cit. p. 19) " each frustule consists of three pieces, one central, ring-like 

 and continuous all romid, and the others lateral." In opposition. Prof. Smitli 

 asserts that the central third segment is no essential part of the frustules, 

 but a portion produced, just like that between the opposed valves of 

 Desmidieae, preparatory to the process of self-fission. 2. '' The division is 

 completed by the formation of new portions within the enlarged central 

 piece, which then falls off, or else by a new septum arising at the centre;" 

 but Mr. Ralfs believes that in every case the separation commences internally 

 before it extends to the covering. So far as we can understand the matter, 

 no essential variation in this process prevails in the two families. 3. " Their 

 coverings, with very few exceptions, are sihcious, withstand the action of 

 fu-e and acids, and may be broken, but not bent ; the frustules are often 

 rectangular in form, are never warted, and scarcely ever spinous." To these 

 statements it may be replied, that in a few Diatoms the silex is in small 

 quantities in the valves, and that, on the contraiy, examples of partially 

 sihcious Desmidieae are known. The action of fire and acids, the capability 

 of being bent or not, are qualities dependent on the relative proportion of 

 silex in the frustules, and are but secondary chstinctions. The same may be 

 said of the remaining points mentioned — the rectangular form, and the 

 presence of warts and spines. The form indeed is, at best, of little value in 



