324 THE JOURNAL OF BOTANY 



greater specialization of the androzoogonidia of the macrandrous 

 forms, are in agreement with the opinions expressed by Hirn/'= 

 concerning the origin of these small male plants. On the other 

 hand, Pascher f states that the nannandrous forms of (Edogonium 

 have not arisen from the macrandrous forms. To the best of my 

 judgment the available evidence does not support Pascher's view, 

 which is largely based upon a comparison with the developmental 

 stages of certain of the Chaetophoraceae. Moreover, it must be 

 distinctly remembered that there is not the slightest evidence to 

 show that there is any phylogenetic relationship between the 

 Ulotrichales and the (Edogoniales. 



I would suggest the following as the possible evolution of the 

 sexual differentiation in CEdogonium : — 



DKECIOUS NANNANDROUS 



Androzoogonidia not more than half the size of gyno- 



zoogonidia ; male filaments small, greatly specialized, 



and localized as epiphytes in immediate vicinity of 



oogonia. 



/|\ 



(E. fonticola (and others ?) 



Androzoogonidia slightly less than gynozoogonidia ; 



male filaments much reduced in size, but not localized 



in position. 



I 



DICECIOUS MACRANDROUS 



Zoogonidia differentiated into androzoogonidia and 

 gynozoogonidia of practically equal size and morpho- 

 logically indistinguishable [although male are often 

 slightly thinner than female filaments] . 



MONCECIOUS SPECIES 



Zoogonidia and filaments hermaphrodite in character. 



One further point of interest in the development of the zoogo- 

 nidia was in the nature of the holdfast. The basal cell of the 

 new plant remains of an elongated-pyriform shape, and the hold- 

 fast is developed in the usual manner, in this type of development, 

 from the colourless, attached end of the original zoogonidium. 

 In those cases where the young plant had become attached the 

 holdfast was only slightly branched (fig. 1, C and D), whereas in 

 the free-floating young plants, all of which were unicellular, the 

 holdfast had the form of a much-branched disc, the branches 

 being marginal, rather narrow, and blunt at the extremities {vide 



* K. Hirn in Acta Soc. Scient. Fennicas, xxvii. 1900. 

 " t A. Pascher, "Uber die Zwergmannclien der CEdogoniaceen." Hedicigia, 

 xlvi. 1906. 



