NOTES ON PONDWEEDS. 379 
segregates, lucens, coriaceus, Zizii and decipiens; or an amended 
lucens carried out on the same principle? In this latter case our 
species will also include heterophyllus, nitens, and one or two obscure 
forms which at present have not attained a place in our British 
catalogues 
eir 
alliances as well as sig: dissimilarities of plants, a method of 
decomposing unwieldy aggregates into subspecies has been adopted. 
But this method is open to the very grave objection that the name- 
form of the aggregate is likely to be mistaken for the type-form, 
and so be misleading to all but those who are well versed in the 
genus. Potamogeton lucens certainly is not the type of the cluster 
of forms we have under consideration, although it is the first-named 
form 
this case, then, it will perhaps be found more convenient to 
relegate the office of expressing alliances to divisional sections or 
groups ; and in spite of the unequal value of our species to give 
each form we have decided upon as worthy of separation, full 
specific rank 
hen 
forms of Pondweeds, when sometimes every ditch seems to have its 
iar form, one is tempted to relinquish the idea of species m 
examination of the variations before us soon shows that they are 
; an 
under the most unusual conditions and in the most extreme forms 
_ we seek in vain for something wholly new to the race. t we 
see accidental conditions seized upon and utilised by the plant, 
which is in no respect compelled to transgress the limits of its 
genus. In a word, design is the factor, not chance. 
Una : 
A single illustration of a temporary variation, not infrequent in 
Pondweeds, may be here given; and itis one that at first sight, 
