232 DESCRIPTION OP {TdhjcjasiAca, 



"Tlie spontaneous division of the frond is included by some 

 writers amongst tlie modes of reproduction, but is rightly the manner 

 only in which the indi^-idual plant grows, since all the cells arrive 

 at maturity nearly at the same period, and terminate their existence 

 about the same time." *' The Besmidieoi are most probably repro- 

 duced only in two modes; one by the escape of the granvdar contents 

 of the mature frond, and the other by the formation of sporangia, 

 the result of the coupling of the cells." 



"^Tien the cells approach maturity, molecular movements may 

 be at times noticed in their contents, precisely like that seen in the 

 Confervse, and which has been aptly termed a sicarming. "When re- 

 leased by the opening of the sutui'e, the granules still move, but 

 more rapidly and to a greater distance. The subsequent histoiy of 

 these granules is, I conclude, similar to what has been traced in 

 other Algae. Compare with this the observations of M. Thuret, 

 which we have appended to the account of Pediastrmn ; for in that 

 genus M. Thui-et states that he witnessed the escape of minute new 

 fr'onds from the cells of the parent fronds. 



On this supposed mode of propagation by Zoospores, we have the 

 advantage of some recent remarks by the Rev. W. Smith : he writes, 

 *' another mode of increase, analogous to the propagation by Zoos- 

 pores in Hpliaroplea crispa and other Algae, has been assigned to the 

 Bemiidiece, and it has been alleged that the endochrome escapes in 

 the form of Zoospores, and becomes transformed into new fi-onds. 

 M. Morren not only affirms this to be the case, but gives a figau'e 

 illustrative of the conversion of these Zoosj)ores, or as he terms them 

 ^' propagules,'" into new fr'onds. Mr. Ealfs merely observes that the 

 escape of the granular contents of the matui'e frond is prohahly one 

 mode by which the Desmidiea; are increased. He, however, regards 

 the " swarming of the granules" (which I am disposed to regard as 

 a disturbance attendant upon the decay of the granular mass) as 

 identical with the movement of the Zoospores ; and states that with 

 the histoiy of these granules after their escape, he ^xas, altogether 

 unacquainted. He afterwards gives a figui-e (British Desmidieae, P. 

 27), upon the authority of Mr. Jenner, representing the bursting of 

 the sporanguim and the growth of the young fronds from its con- 

 tents in Chsterium acerosium, so closely resembling the figiu'e by 



