Closterium Ehrenbergii. 5 



midiese, pi. 27), upon the authority of his coadjutor Mr. Jenner, 

 representing the bursting of the sporangium and the growth of 

 the young fronds from its contents in Closterium acerosumy so 

 closely resembling the figure by M. Morren of the conversion of 

 the propagules of Closterium Ehrenbergii into young fronds, that 

 I cannot but believe a similar phsenomenon to have been noticed 

 by both observers, and am incHned to accept the view of Mr. Jen- 

 ner as the correct one, and to regard propagation by zoospores 

 or '^ propagules " as one not yet satisfactorily established in the 

 Desmidiece. 



Increase by self-division, where a single frond separates into 

 two equal parts, and generates at the suture two new segments 

 respectively attached to the old, and thus forms from itself two 

 perfect fronds, is one mode by which these minute organisms 

 multiply with amazing rapidity ; but this is merely a repetition 

 or increase of the individual ; the species must be renewed by 

 another method, and that 1 believe to be the result of conjuga- 

 tion, or in other words, the conversion of the sporangial contents 

 into young fronds ; the subject however still requires elucidation 

 from the cautious and skilful use of the microscope. 



I may remark in conclusion, that in a generic arrangement, 

 based upon the reproductive organs, Closterium Ehrenbergii will 

 stand apart from all other Desmidiece. In it alone a pair of con- 

 jugating fronds produce two sporangia. It is however allied to 

 others of the present genus through Closterium lineatum, the spo- 

 rangium of which, according to Mr. Ralfs, is binate, and shows 

 a disposition to separate into two parts. 



Wareham, November 1, 1849. 



EXPLANATION OF PLATE L 



Fig. \. A single frond of Closterium Ehrenbergii in its ordinary condition. 

 Fig. 2. Two fronds approaching and in the apposition which precedes con- 

 jugation. 

 Fig. 3. Conjugating fronds undergoing self-division, the upper showing the 

 protuberances through the torn apices of which the contents of the 

 divided fronds pass into the sporangia. 

 Fig. 4. Conjugating fronds showing the {)assage of the endochrome-sac and 



its contents. 

 I'ig. 5. Conjugated fronds having perfected their sporangia. 

 Fig. 6. Development of the " propagules " into young fronds (after Morren). 

 Compare with the figure given in the ' British Desmidieje,' pi. 27, of the 

 conversion of the sporangial contents into young fronds in Closterium 

 acerosuin. 

 Fig. 7. a, b, c, d. Development of a sporangium into " uneClosterie a deux 

 cones inegaux," from Morren. 

 The figures aie all magnified 100 linear. Length of ordinary frond V^ of 

 an inch ; greatest breadth of ditto -^^ ; length of divided frond j^^ ; 

 length of beak ^^ji\ diameter of spoiangiuni s^-^. 



