112 



Rhodora CJ UNR 



older genus Conferva which have fronds composed of repeatedly 

 branching, monosiphonous, articulated filaments. The fruit in all 

 is substantially the same ; the contents of practically any cell in the 

 frond may be transformed into numerous zoospores, which escape 

 through an opening in the side wall. The shape of the cell is only 

 slightly if at all changed in this process. Kjellman x has attempted 

 to use characters derived from these fruiting cells for the distinction 

 of species among the Scandinavian Cladophoras, but it is doubtful 

 if the characters he uses will be found available generally. There 

 remain for distinction only vegetative characters ; —the size of the 

 frond as a whole, the diameter and length of cells in the main fila- 

 ments and their branches; the arrangement of the latter, alternate, 

 opposite, whorled or secund ; the angle at which they issue ; their 

 straightness or curvature, acuteness or bluntness; the shade of 

 color; and finally, the presence or absence of special rhizoidal or 

 spinous branches in addition to the normal ramification. All these 

 characters vary much according to external conditions, and also 

 with the age of the individual plant, so that a knowledge of a species 

 as it appears in different environments, and an acquaintance with 

 all stages of growth are necessary before an attempt can be made 

 at drawing specific lines. Add to this the fact that most of the 

 species seem to be still in an evolutionary state, and connected by 

 innumerable intermediate forms, and it will be seen that the identifi- 

 cation of a specimen with some one of the 300 described species, 

 often very loosely and insufficiently characterized, is no easy matter. 

 On the other hand, there is the advantage that none of these 

 characters requires careful microscopic study. In most cases a 

 pocket lens will give all the characters needed, and in some cases 

 even the pocket lens is unnecessary ; while a magnification of 40 or 

 5 o diameters will furnish all that can be needed in any case. The 

 trouble is not in perceiving the characters, it is in keeping in mind 

 the type for each species, and deciding what relative weight to give 

 to apparently contradictory characters ; to decide what is really 

 characteristic of the species, what due to external conditions. 



The number of species occurring on the New England coast is 

 quite limited, but even as to these few the lines of demarcation are 



-Studier ofver Chlorophyc6slagtet Acrosiphonia J. G. Ag. och dess Skandi- 

 naviska Arter. Bihang till K. Svenska Vet.-Akad. Handlingar, Band. 18, Afd. 

 Ill, No. 5, Stockholm, 1893. 



