28G DESCRIPTION OF {Fohjgostrica. 



The process of division takes place at the notch, as in other 

 BesmidiecB. 



M. Thuret has recently advanced the statement, founded on his 

 personal observation, that the fronds of Pediastrwn elliptmim de- 

 vclope vrithin their cells exact but miniite copies of themselves ; 

 which, in course of time, assume the size and all the characters of 

 the parent. He says, " all doubt was removed fi'om my mind, when 

 I witnessed the escape of four young ones from the cells of an old 

 frond : the cells opening and emitting by degrees, often by jerks, the 

 young Pediastnmi, enveloped in its gelatinous mass." Cinn. des 

 Sciences Nat. 1850.) 



The old cells are left empty and colourless. In fi'onds not very 

 young, a clear nncleiis, refracting light strongly, was discernible ; in 

 the very young, this is not visible, and in the old fronds very indis- 

 tinct. M. Thuret believes it to be concerned in the formation of the 

 cell, or the reproduction of the species. 



This method of development (M. Thuret remarks), rccals that of 

 Vol/vox globator, and of other Infusoria ; and is probably without 

 analogy among plants, (with which I reckon Pediastrum.) See 

 observations of Weiss on Chlorogonium euchlorum, p. 192. 



Elu-enberg has named this genus Miorasterias, who characterizes 

 it thus — by their members being free, by their having a simple 

 compressed lorica, composed of one piece, and grouping themselves 

 together in definite numbers, in the fonn of a flattened star. The 

 latter generic character arises from incomplete self-division when 

 they are young, like Gonium. Projection organs of locomotion 

 have not been observed, though slow change of place has been 

 noticed. Numerous vesicles, analogous to polygastric digestive cells, 

 are seen in several species; ova-like green granules are abundant; 

 and Ehi'cnberg states he has seen glandular bodies which periodically 

 increase in size, and ai*e analogous to the seminal glands of other 

 Infusoria. The dispersion of the ova has been seen by Tui-pin and 

 Meyen, though it was regarded by them as that of the fecundating 

 matter of plants. Dr. E. appends the following observations to the 

 genus : — 



"1. The relations of number observed in Micrasterias appear to 

 form a tii-m character of the species (as in Gonium pectoralc.) 



