4 Rev. W. Smith on the Conjugation of 



thing with certainty. I preserved a mass of the conjugated 

 fronds and multitudes of the perfect sporangia in water, which I 

 frequently changed, for more than four months, but could not de- 

 tect any appearance of young fronds, nor did I notice any mate- 

 rial change in the sporangia until decomposition supervened with 

 the increased temperature of the season. 



M. Morren contends that a sporangium becomes converted 

 into a single frond, and gives a series of figures in illustration of 

 the changes which the sporangium undergoes until it becomes 

 " une Closterie a deux cones inegaux" (fig. 7 a,b,c,d). Now as I 

 have shown that this form is the result of the self-division of the 

 ordinary frond and invariably precedes conjugation, I am disposed 

 to think that M. Morren has mistaken fronds thus divided, and 

 afterwards thrown out of their relative positions, for modified 

 sporangia. Certain it is that among myriads of conjugated 

 fronds and their sporangia I have been unable to trace the gra- 

 dations figured by M. Morren, nor have I on any occasion de- 

 tected the slightest modification in the sporangia after their full 

 maturation. A divided frond smaller than the others, or one in 

 which the self-division has been arrested, may occasionally be 

 discovered, but the very rarity of such examples precludes the 

 idea that such forms result from the normal development or 

 growth of the sporangia. 



How the species in Closterium Ehrenbergii may be renewed, 

 appears still involved in the same uncertainty as that which en- 

 velopes the propagation of every other species of Desmidiece. Self- 

 division in the case before us seems only to accompany conju- 

 gation, and will not, as in the other Desmidiece, account for the 

 existence at certain periods of vast multitudes of the fronds. 

 Another mode of increase, analogous to the propagation by zoo- 

 spores in Sphceroplea crispa and other Algse, has been assigned 

 to the Desmidiece, and it has been alleged that the endochrome 

 escapes in the form of zoospores, and becomes transformed into 

 new fronds. M. Morren not only affirms this to be the case, but 

 gives a figure illustrative of the conversion of these zoospores, or 

 as he terms them " propagules," into new fronds. Mr. Half's 

 merely observes that the escape of the granular contents of the 

 mature frond is probably one mode by which the Desmidiece are 

 increased. He however regards the " swarming of the granules " 

 (a curious circumstance observable in the Desmidiece and other 

 Alga?, and which I am disposed to regard as a disturbance at- 

 tendant upon the decay of the granular mass) as identical with 

 the movement of the zoospores, and after accurately describing 

 the phenomenon, goes on to state, that with the history of these 

 granules after their escape from the frond he was altogether un- 

 acquainted. Mr. Ralfs afterwards gives a figure (British Des- 



