66 



Wheldon : The North of England Harpidia. 



The plants of this section of the great genus Hypnum are of 

 much interest on account of their variety of form and the fceauty 

 of many of the species. They present one of those natural 

 associations of closely allied forms which are looked upon by 

 the mere collector as stumbling-blocks, and dubbed 'critical/ 

 but which are of the highest interest to the real student, the 

 continuity of the chain of forms permitting- the study of the 

 origin or limitations of species under the most favourable con- 

 ditions. 



The Harpidia are usually readily distinguished from their allies 

 by their tall erect or floating stems, often pinnately branched, 

 without tomentum or paraphyllia, usually hooked at the apex of 

 stems or branches. The leaves are more or less falcate-secund 

 or circinate, generally with fine points, and the cells linear 

 above, at basal angles shorter subquadrate, more or less 

 inflated, and frequently forming well-marked auricles. Their 

 tints vary through all the shades of green, yellow, brown, red, 

 and purple, and they are sometimes very richly coloured. Nearly 

 all the species grow in bogs, pools, and marshes, and their 

 appearance is often greatly modified by the nature of the habitat, 

 as is frequently the case with aquatic plants. This variability 

 and the occurrence of numerous transition forms between the 

 groups renders their determination unusually difficult. Mons. 

 Renauld emphasises the fact that it. is impossible to satisfactorily 

 name all such intermediate states. He says in a recent letter 

 that ' pretendre distinguer et nommer toutes le formes qui ne 

 correspondent pas completement aux varieties principales est 

 une pure chimera et, en suivant cette method, on arriverait a la 

 distinction de la form individuelle, c'ut a dire au cahos.' Sanio 

 and other Continental botanists have endeavoured to define 

 hybrids, and the system of classification adopted by the former 

 is partly based on the occurrence of hypothetical hybrids. 



It will be observed that the definition of Harpidinm g-iven 

 above excludes those plants (Cratoneurori) distinguished by 

 having stems clothed with paraphyllia or tomentum. I have 

 followed Mons. Renauld in retaining H. scorpioides, and with 

 him have rejected H. callichroum, which is placed by Sanio after 

 H. uncinatum. 



For the purpose of preservation, good and liberal specimens 

 should be collected, so as to show the habit of the plants. 



I have found that the principal forms and varieties main- 

 tained by Mons. Renauld, if of somewhat unequal value, 

 nevertheless truly represent types that frequently recur, and 



Naturalist; 



