OF NORTHUMBERLAND AND DURHAM. Td 
it constitutes the Byssus purpurea of old authors*. In the Haw- 
thorne locality, however, it attains a size larger than usual even 
in favourable situations; so that the fresh water cannot be sup- 
posed to exercise any prejudicial influence on its growth. Now, 
it so happens that there is another genus described by algologists, 
(Trentepohlia) which, according to Professor Harvey, differs from 
Callithamnion in no other respect than its fresh water habitat. 
Indeed, in the first edition of his ‘‘ Manual of the British Alge,” 
he remarks “that C. Daviesti and T. pulchella, when the latter 
is well coloured, are scarcely distinguishable under the microscope.” 
It seems to me that the Hawthorne plant goes a great way to 
establish Dr. Harvey’s view of the identity of the two genera, 
for though exposed for about sixteen hours out of twenty-four 
to the influence of fresh water, it is certainly referable to the 
marine species Callithamnion Rothii, and at the same time is 
undistinguishable, so far as I can gather from figures and written 
descriptions, from the fresh water species Trentepohlia pulchella. 
There is nothing exceptional in the case of a plant growing 
indifferently either in salt water or in fresh. The common 
Enteromorpha intestinalis, a marine species, flourishes in streams, 
ponds, and ditches quite away from sea influence. Bangia fusco- 
purpurea has been found in like circumstances ; and even with 
animals, instances of a similar tolerance might be brought for- 
ward. In short it seems quite unphilosophical to separate plants 
which are to all appearance precisely similar, merely on account 
of a difference in habitat; for what does such a circumstance 
show, more than that a single species possesses the capacity of 
of existence under widely different conditions ? 
* Byssus purpurea is noted by Mr. Winch as occurring “on rocks and stones in alpine 
situations.” Assuming that the plant alluded to is the same as that found on rocks with 
marine exposure (which, though evidently inferred by Mr. Winch, is perhaps reasonably 
open to doubt) there seems the less reason to hesitate in uniting the two aquatic forms. 
But without further evidence of the identity of the two terrestrial plants it is impossible to 
push this argument, 
