Wheldon : Key to the Harpidioid Hypna. 19 



maintained, this may be regarded as a venial sin compared 

 with that of making a too sweeping reduction of their number. 

 The older botanists in England looked askance at the intro- 

 duction of new varieties, whilst their continental confreres 

 perhaps erred in the opposite extreme . The result in this 

 country was that there was a constant effort to fit square pegs 

 into round holes ; and our older herbaria sometimes contain 

 an incongruous admixture of different forms under one label. 

 Many of the minor forms described in continental works are 

 of little importance, but their lists present perhaps a truer 

 and more natural view of this polymorphous group than that 

 of our own botanists of the last generation. 



The arrangement adopted here is in some respects a com- 

 promise between that of the 'North of England Harpidia,'^ 

 adopted from Renauld,'^ and that of Loeske.^ Some of the 

 larger and more polymorphous species have, as a matter of 

 convenience, been divided into sub-species. On the other 

 hand the old Drepanocladus Kneiffii and D. polycarpus have 

 been merged, as previously suggested by me, ^ as no satis- 

 factory or constant line of demarcation can be drawn between 

 them. D. aquaticus has been subordinated to D. pseudofluitans 

 in preference to regarding it as a distinct species, or as a 

 variety of D. adunctis. Warnstorfia serrata is doubtfully 

 maintained as a species until it has been studied further. 

 From my limited experience of it, its two forms Lindbergii 

 and Mildei have no constant differential characters apart 

 from the inflorescence, and this is not always available. Their 

 case is analagous to that of Bryiini pseudotriquetrum and B. 

 himiim. Renauld ^ regarded one as a fluitans and the other 

 as an exannulatum form. I follow Renauld and Monkemeyer * 

 in rejecting Drepanocladus simplicissinius , although Roth ^ 

 follows Warnstorf in giving it full specific rank. I agree 

 with Renauld ^° and Dixon ^ that D. capillifolius should be 

 maintained as a species, although Monkemeyer "* gives some 

 cogent arguments against this course. It follows, to be 

 consistent, that Warnstorfia Rctae should be considered to be 

 distinct from W. exannulata. I have not been able to see a 

 specimen of Hypnum fluitans var. Brotheri Sanio. ^^ 

 Renauld ^ does not attempt to indicate its affinities with his 

 various fluitans groups, but Roth ^ puts it near var. Arnellii 

 and indicates some features in which it approaches W. exannu- 

 lata. It may be remarked that Renauld figures it with a 

 finely acuminate leaf point, and describes it as ' Feuilles fine- 

 ment acuminees munies au sommet de petites dentes espacees.' 

 Roth, on the contrary, says : ' mit ganzrandigen, kurz and 

 breit zugespitzen Blattern.' Sanio's original description is 

 as follows : ' foliis acutis acuminatisve, repandulis vel apice 

 singulis denticulis serrulatis.' I have not attempted to place 



1921 Jan. 1 



