108 REPORT OP BRITISH COMMISSIONERS. 



382. To render tlie meaning' of tliis fact clear to those wlio liavo not 

 particularly paid attention to this subject, the following (juotation may 

 be given from the article on lichens in the " Encycloptedia Britannica'' : * 



In this fitful iind abnormal life of lichens, we have the explanation in a ^reat 

 nieasnre of tlicir almost indelinite duration of existence. It is well known that they 

 are perennial ])lant8 in the widest sense of this term ; and that, though in the earlier 

 stages of their existence, their growth is comparatively rapid, yet this becomes 

 extremely slow when they arrive at a certain age. The time required for the devel- 

 opment of even the most rapidly growing species may be calculated by the apjx'ar- 

 ances of such of these as are met with on gravestones, mortar of houses, stone walls, 

 Avooden palings, and such like, the date of wliose erection is known. Amongst other 

 instances that have come under the present writer's own observation maj' be adduced 

 the case of rin/scia parietiiKi [the common grey lichen of the Pribyloff Ishmds is a 

 Fln/scial, growing in fair quantity on the stones of a granite wall, built in 1838, in 

 a maritime district where the plant is extremely abundant, and where tlie atmos- 

 pherical and other conditions are well suited for its growth. In a recent visit to the 

 spot, it was found that although the thallus is now well dev(?loped,no fructilication 

 whatever is visible, though traces of spermogones are beginning to appear, so that, 

 in a space of forty-five years, this plant has not yet attained full maturity. 



383. Still another characteristic of the rookery grounds is, that their 

 surtaces are generally composed, especially in hollows subjected to little 

 wear, of a felted coat of mud and hair. In the damp climate of the 

 Pribyloff Islands this characteristic does not endure very long, and 

 when any particular area is abandoned for a few years by the seals, it 



soon becomes again covered with grass. 

 G9 384. This last circumstance leads to the consideration of a fact, 



ui)on which much stress has lately been laid, in connection with the 

 estinnition of the present and firmer areas of the rookeries and hauling 

 grounds. It is quite noticeable that when an area doubtless originally 

 covered with rough, tussocky grass of long growth, and of the character 

 normal to the islands (and generally or always confined to the single 

 species, Ehjmvs mollk)^ has been occupied by seals for such a time as 

 to eradicate this grass and smooth down the lumpy surface upon which 

 it grew, the tem})ora.ry or permanent abandonment of the area is followed 

 by the appearance on it of grasses of a shorter and closer growth, and 

 which in the later summer and autumn sooner assume yellowish colours, 

 in consequence of which the outlines of the previously occu}iied area 

 become clearly defined. It is quite natural, that in the unfortunate 

 absence of any consecutive record of the extent of the rookery grounds, 

 or of correct or comparable estimates of the number of seals upon them 

 or upon the islands as a whole, these "grass limits," as they may be 

 called for brevity, have been seized ui)on as something tangible. 



385. The "grass limits" are often quite readily observable, particu- 

 larly from a little distance, and some special attention was given to them 

 in order to ascertain, as far as possible, to wiiat extent they might be 

 employed as a criterion of change, and particularly of diminution in the 

 areas frequented by seals, or in the aggregate number of seals resorting 

 to the islands. 



386, It may be mentioned, in the first place, that the grasses to be 

 found in these particular areas are not in themselves peculiar, but it is 

 merely the predominance of certain forms and their mode of growth 

 which seems to outline such areas, the most abundant grass being 

 apparently Descltamima {Aira) cocsjntosa, with which the little crucifer- 

 ous plant Cochlearia officinalis is often mingled. Farther, that a very 

 similar growth and colouration is found in other x^ai'ts of the islands, 

 which have never been known to be, and which in all probability never 

 have been, frequented by fur-seals; as, for instance, on the easterly 



* Ninth edition, vol. xiv, p. 558. 



