ARCHER, ON DESMIDIACE.E. 225 



adult Closterium, and farther increase in dimensions follow- 

 ing, tmtil the full size of tlie species is attained. He, more- 

 over, describes the act of conjugation (since accurately de- 

 scribed by Smith, /. c.) ; but, strange to say, he (M. Morren) 

 does not seem to look upon this as a true generative act, so 

 far as I can judge, but seems to think the sporangium (" semi- 

 nule") resulting from the act of conjugation is itself ferti- 

 lized during the process by the agency of the at first terminal 

 motile particles. He states the further development of the 

 spherical sporangium (itself as great in diameter as the old 

 frond), previously undergoing a revolving motion for a few 

 moments, to consist merely in its gradual elongation in two 

 opposite directions, but unequally, thus forming two unequal 

 cones. It is to be supposed, however, that he must imagine 

 the smaller cone would eventually keep up with the longer, 

 so as to restore the symmetry. Such is, briefly, Morren's 

 account of the reproduction in this plant. 



Professor Smith (/. c.) gives a nearly similar account of the 

 process of conjugation. The conjugative act in this species is 

 not undertaken till after the two original fronds about to cdn- 

 jugate have undergone self-division in the manner usual in 

 this genus — that is to say, by self-fission, effected by a divi- 

 sion of the contents into two just under the suture, accom- 

 panied by a development of new cell-wall to each old segment, 

 and separation taking place. The separated portions have 

 now one long (and old) cone, and one more blunt and rounded 

 (the nascent younger one) . Now, in those individuals about 

 to conjugate, from each of the shorter or younger cones is 

 protruded a blunt, pouch -like projection from the lower and 

 opposed sides of each, which approaching by gradual growth, 

 the contents from each emerge thereby, and, meeting half 

 way, amalgamate with each other; at the same time the 

 other opposite portions of the original parent fronds doing in 

 precisely the same manner. Thus two sporangia ultimately 

 result from the two original fronds, conjugation taking place 

 between each of the opposite individualized pairs of partially 

 old, partially new, fronds — themselves resulting from the 

 self-division of the original parent fronds. A parallel pheno- 

 menon is furnished in the process of conjugation by Closterium 

 lineatum, as well as by several diatoms. Professor Smith was 

 not able to see any further development of the sporangium, 

 and the propagules of Morren, he believed, had no existence 

 in fact. 



I believe the explanation of Alorren's statement to be 

 possibly something like the following : — From researches of 

 recent date in regard to the after development of the sporan- 



