Cr | REVUE BRYOLOGIQUE 
grade as « subspecies ». Until we are more familiar with their 
ancestry the better course would seem 10 be to class them all as 
species. Subordinating one species to another necessitates a deci- - 
sion us to which shall be subordinate. Do we always know this? 
Who can decide whether the group discussed in this paper should 
be subordinated to 77. lycopodioides or to H. aduncum ? 
The creation of large, unwieldy aggregate species, whilst 
apparently simplifying matters, will really complicate them. Many 
records will become useless because of the difficulty of discove- 
ring whether a name is used in an aggregate or segregate sense. 
The relationship of the species dealt with in this paper can be 
. equally well shown by grouping them as a subsection of the 
 Harpidia, and, it seems desirable to carefully refrain from giving 
them an aggregate specific name. À name should be limited to 
its proper function, that of fixing the identity of an object, and 
any attempt to make it express Loo much is apt to lead to compli- 
cations. The old Linnean conception of a species, as something 
having certain distinguishing characters imprinted upon it ab 
iniho, is difficult to get awav from. Under later conceptionsoneis 
led to expect a chain of forms linking the species together. When 
the links are lost, or at all events undiscovered, the species seem 
distinct, In the group called by Sanio the « Harpidia adunca » 
they are found in such profusion, and diverge in so many Oppo- 
site directions as to bewilder the taxonomist, and teach him the 
utter impossibility of arranging his forms in the lineal sequence 
Of the orthodox catalogue. Hypnum aduncum itself, the type of 
the group, shows how difficult is the task of defining the limits of 
the species in mosses. Warnstorf regards Hypnum pseudofluitans 
as à distinct species ; Renauld considers it to be a group of varie- 
ties under 7. aduncum, without even subspecific value; and 
M' Ingham, in a recent paper in the Revue Bryologique (4908, 
p_38) implies that itis a mere submerged state of Æ. aduncum 
 (£ypicum). reverting under drier conditions to that form of the 
species. +. ; 
It is this last article, dealing with the varietal forms of A. adun- 
cum and its allies in a Yorkshire locality, which leads me to offer 
these comments on a similar subject, more especially as my expe- 
rience and observation do not lead me to the same conclusions | 
as those arrived at by Mr Ingham. To adopt the view he expresses, 
‘which is diametrically opposed to that of Warnstorf, the latest. 
__ exponent of the group, something like a revolution would be 
required in the nomenclature of these plants. 
In considering M' Ingham's remarks, one must grant what 
