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 & deux cones inégaux” (fig. 7a, b,c,d). NowaslI 
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 Desmidiee. Self- 
division in the case before us seems only to accompany conju- 
gation, and will not, as in the other Desmzdiee, 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 Spheroplea crispa and other Algz, has been assigned 
to the Desmidiee, 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. Ralfs 
merely observes that the escape of the granular contents of the 
mature frond is probably one mode by which the Desmidiee are 
increased. He however regards the “ swarming of the granules” 
(a curious circumstance observable in the Desmidiee and other 
Algee, 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. ir. Kalfs afterwards gives a figure (British Des- 
