86 BRITISH CHAROPHYTA. 



The counties and vice-counties cited under the 

 several species are those from which we have actually 

 seen specimens, with a very few exceptions, and in 

 these the authorities are stated. It has not as a rule 

 been considered safe to depend on printed records, so 

 many extraordinary cases of incorrect determination 

 having occurred, even by botanists of high standing. 



In the arrangement of genera and species we have 

 in the main adopted that of Braun and Nordstedt's 

 6 Fragmente,' but have followed Professor Hy in 

 separating Nitellopsis from Lychnothamnus, and, 

 among the Charge diplostephande diplostichde, have 

 placed the sub-section aulacanthae before the t-yla- 

 canthae, since among British species some of the 

 latter appear to be more nearly allied to the section 

 triplostichde than any of the former. No linear 

 arrangement can be entirely natural, and the separa- 

 tion of some closely allied species (e.g. C. vulgaris 

 and C. contrariety is inevitable. 



We have adopted the designations Anarthrodactylae 

 and Arthrodactylse for the primary divisions of Nitella 

 in preference to those employed by Braun, viz. 

 Monarthrodaclylse, DiarthrodaGtylae, and Pohjarthro- 

 dactijlse, for the following reasons : the first of 

 Braun' s names does not appear to be etymologically 

 correct for the purpose to which it is applied, the 

 " dactyl," i.e. the ultimate ray, not itself possessing any 

 joint, though jointed to the limb below. The human 

 finger could hardly be described as one-jointed, if 

 it had but a single bone. Similarly Diarthrodactylse 

 is open to objection, since normally the 2-celled 

 "dactyl' has but one joint or division. We combine 

 Braun's second and third sections in view of the 

 difficulty of drawing a satisfactory line between 

 them. We have not adopted Professor Hy's sections 

 FuTcinitella and Garni tella, as .the characters upon 

 which they are based can be applied to European 

 species only. 



The Charophyta are extremely plastic, most species 



