22. BRITISH MARINE ALG. 
decided rarity of this genus is the very delicate species B. hypnoides. I 
have found this plant at distant intervals of time and in widely different 
situations. For instance I met with it at Plymouth about twelve years 
ago, and in tolerable plenty; but in subsequent visits to the same locality 
I never saw a single 
specimen of it. At 
Torquay I hunted for 
it in vain for three 
seasons, when all at 
once I discovered it 
by the merest chance, 
growing in a rock pool 
at high water mark 
near the abbey rocks 
in Torbay. This ap- 
pearance and dis- 
appearance of certain 
species of seaweeds is 
certainly very remark- 
able, and opens out a 
wide field of specula- 
tion on the probable 
causes of this singular 
caprice in the growth Fic. 25. Bryopsis hypnoides. 
and irregularity of 
appearance in marine alge. I have endeavoured in vain satisfactorily to 
account for it, but experience has pointed out to me two probable causes. 
In the first place I consider the disappearance of some species of rare sea- 
weeds is due to the rapacity of inconsiderate collectors, who, when they 
meet with a rare plant, instead of being content with a portion of it, and 
leaving sufficient for the chance of its bearing spores, and thus producing 
a new crop, ruthlessly seize every specimen upon which they can lay their 
hands, and thus the species is lost, at least for a time. This, I am con- 
vinced, is the most general cause for the disappearance of some species, 
and another may probably be due to the fact that the plants, although 
growing in tolerable luxuriance and abundance, may not have been in fruit, 
and consequently perished without having been able to propagate their 
species. 
The genus Bryopsis is ordinarily represented by the justly-admired 
species Bryopsis plumosa. Its companion, B. hypnoides (Fig. 25), is equally 
beautiful, much more delicate in its growth and general appearance, and is 
certainly a rare plant ; indeed, I have heard more than one collector doubt 
that it existed otherwise than as a book species, or, at most, a permanent 
variety. One autumn I took one solitary specimen of the little gem, 
leaving a considerable portion of it still growing on a plant of Corallina 
officinalis, in an out-of-the-way rock pool. The following season I was 
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