OF THE DESMIDIEiE. 21 



scribed: we have noted their process of reproduction and of growth, the 

 molecular and circulatory movements within them, their slight locomotive 

 power ; but besides these, there are others requii'ing to be mentioned : for 

 instance, their powers of secretion are highly pronounced ; — the production 

 of firm envelopes to fronds and sporangia ; the formation of starch-grains, of 

 colouring matter, and of oil-globules within ; the exhalation of oxygen from 

 the surface, — a respii^atory act ; and lastly, their ability to resist decomposition. 



The Desmidieae serve as food to many sorts of small aquatic animals, to 

 the Rotifera, to various Annelida and small Ciiistacea, and to the fi^eshwater 

 Mollusca. They are supposed also to preserve the freshness of the water, 

 and by the oxygen they exhale, to fiu'nish the vital air necessary to the 

 respii'ation of the aquatic animals found Avith them. They are subject to 

 destraction not only in the way of supplying food to animals, but also by 

 disease. For instance, Cohn has shown (Enhu. d. mih\ Alg.) that the 

 Closteria are attacked by a microscopic unicellular fimgus, called Ohytridiiim, 

 the spores of which affix themselves on the integument, and on germinating, 

 penetrate the cavity of the frond by their delicate fibres, and induce a pro- 

 gressive breaking-up and absorption of the contents, until nothing but the 

 empty hull of the plant remains. 



Mr. Ralfs has the following remarks (p. 13) : — '^ In all the Desmidieae, but 

 especially in Clostenum and Micrastenas, small, compact, seed-like bodies of 

 a blackish colour are at times met "with. Their situation is uncertain ; and 

 their number varies from one to four. In their immediate neighboui^hood the 

 endochrome is wanting, as if it had been requii^ed to form them, but in the 

 rest of the frond it retains its usual character and appearance. I cannot 

 satisfy myself respecting the nature of these bodies ; but I believe them to 

 arise from an unhealthy condition of the plant, or else to be parasitic." With 

 respect to the views expressed in this extract, we are disposed to think Mr. 

 Ralfs right in his conclusion that the black bodies he met with were parasitic ; 

 and on comparing his account ^yith. the figures and description of the parasitic 

 Chytridium in Cohn's memoii^ (Enhv.), it seems to us highly probable that the 

 globules referred to were no other than the spores of that microscopic fungus. 



Tor a long time discussion was rife respecting the animal or the vegetable 

 nature of the Desmidieae. That it was the former was the prevailing 

 notion until within the last few years, when the improvements in the 

 microscope, and the more extended and accurate knowledge of the features 

 of vegetable life in its simplest manifestations, rendered this opinion no longer 

 tenable, and at the present day it may be considered exploded. It is un- 

 necessary, therefore, to go minutely into this question ; for it will suffice to 

 indicate the most striking distinctive characters, especially those which rest 

 upon the affinities of the family under consideration. Those readers who 

 would see the point fully discussed will do well to refer to Mr. Ealfs's admi- 

 rable monograph, to which we, and others also, resort as to a mine, for the 

 materials to build up a histoiy of the Desmidieae. 



An old argument advanced by Ehrenberg for the animality of the Des- 

 midieae, was, that they had a power of voluntary movement like animals. 

 Without staying to consider the loose and unphllosophic use of this term 

 voluntary, as applied to the motion, whether in the Desmidieae or in the 

 simplest animal existences, its occurrence can be no proof of animal life, 

 seeing that it is exhibited by acknowledged plants, and in a still more marked 

 manner by their spores. Moreover, such movements are doubtless effected 

 by cilia, both in the animal and vegetable world alike, and are likewise 

 determined by the vital processes going on within and also mthout these 

 simple organisms, in relation with external media and ^dth surroimding 



