Closterium Ehrenbergu. 5 
midiez, pl. 27), upon the authority of his coadjutor Mr. Jenner, 
representing the bursting of the sporangiuin and the growth of 
the young fronds from its contents in Clostertum acerosum, so 
closely resembling the figure by M. Morren of the conversion of 
the propagules of Closterium Ekrenbergii into young fronds, that 
I cannot but believe a similar phenomenon to have been noticed 
by both observers, and am inclined 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 
Desmidiee. 
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 I 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 Desmidiee. 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 I. 
Fig. 1. 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 passage of the endochrome-sac and 
its contents. 
Fig. 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 Desmidiez,’ pl. 27, of the 
conversion of the sporangial contents into young fronds in Closterium 
acerosum. 
Fig. 7. a,b, c,d. Development of a sporangium into “ une Closterie a deux 
cones inégaux,” from Morren. 
The figures are all magnified 100 linear. Length of ordinary frond +; of 
an inch; greatest breadth of ditto 33; length of divided frond 73, ; 
length of beak .3,,; diameter of sporangium 444. 
