22 GENEEAL HISTORY OF THE rNTUSOEIA. 



physical conditions. Siebold, quoting Nageli's opinions, says (J. M. S. i. 

 p. 120) — " The slow turning, and at the same time rare movements of the 

 Closteria (the genus in which motion is more evident), present no character 

 of spontaneity; these motions are merely the consequence of an active 

 endosmosis and exosmosis, by which the water immediately surrounding the 

 Closteria, and consequently themselves, are put into motion." Again, as Mr. 

 Ealfs remarks, the motive power is less in degree than in the Diatomece. 



Cell-multiphcation by fission or transverse division, enumerated by Ehren- 

 berg as an animal peculiarity, is now so completely established as a vegetable 

 phenomenon, that it can claim no consideration when the question of the 

 actual affinities of a disputed organism is to be solved. And equally unde- 

 serving of critical examination at the present day is the complex animal 

 organization attributed by the Berlin microscopist to the fronds of Desmidieae. 

 Concerning the apparent sac containing the moving particles in the Closteria 

 and in other genera, regarded by Mr. Dahymple as a vegetable peculiarity, 

 Mr. Ralfs observes, " I confess I am unable to refer to any example in other 

 Algae of terminal globules like those present in the Closteria, but neither can 

 one be found amongst animals ; and if in some respects they have an analogy 

 with organs belonging to the latter, in others they agree better mth vegetable 

 life." On another argument raised, the same author remarks, " The eon- 

 traction of the internal membrane of the Closteria, or the expulsion of their 

 contents on the application of iodine or other reagents, cannot be rehed upon 

 as a satisfactory test for determining their nature ; for the blandest fluids will 

 in some cases (both among recognized Algee and the Closteria themselves) 

 occasion \iolent action." On the other side of the question, the act of swarm- 

 ing, the emission of actively motile germs (presumed in this family), the 

 presence of starch and of chlorophyll, the chemical relations between these 

 substances, and also \\'ith the oily matters formed in the fronds, the exhala- 

 tion of oxygen in sunhght, and the absence of azotized material in their 

 chemical constitution furnish reasons for arranging the Desmidieae with 

 plants. Besides these reasons, others are found in the general form and in 

 the modes of propagation being precisely analogous with those in admitted 

 unicellular Algae. Theu- intimate affinities with Alga3 are shown by the fact 

 that Meneghini and Kiitzing placed Metnsmopcedia among the Desmidieae, 

 and that Braun refers the two genera Scenedesmiis and Pediastrum, included 

 by Ehrenberg himself in the family in question, to the Palmellaceae. The 

 process of conjugation, which has been often appealed to as a characteristic 

 of plant-life, would appear, however, to be, in exceptional cases and under 

 peculiar modifications, also an animal phenomenon, and therefore inapplicable 

 as a test. 



Meneghini, who contends for the animality of the Diatomeae, has pro- 

 nounced {B. S, p. 497, 1853) the opinion that — " The Closteria and Des- 

 midieae in general are plants, and not animals. In the actual state of science 

 we are compelled to admit this proposition. The organic structui'e, the phy- 

 siological phenomena, the history of their development, the chemical materials 

 they contain, manifest in these beings a perfect correspondence with others, 

 which in every point of view correspond with the abstract idea of a plant. 

 But what they present in common with other beings evidently animal, is 

 merely an appearance, or at the most, a resemblance in external form. 

 Ehrenberg was misled by this appearance, and, guided by this fallacious 

 similitude, thought that he discovered in the Desmidieae the same organic 

 pecuHarities which proved the animahty of other beings." 



Kespecting the affinities of the Desmidieae, Mr. Ralfs states that, " on one 

 side, they are allied to the Conjugatae (Zygnemeae) by similarity of reproduc- 



