522 G. T. HARRIS ON MICROSCOPICAL METHODS 



They are not in the least particular where they grow, any 

 ineligible site will do for them. The only disturbing factor in 

 the life of a moss that I am acquainted with is an east wind. 

 They will stand all the indignities that man in the shape of an 

 agricultural labourer can inflict upon them, but with an east 

 wind they make no manner of compromise, they shrivel up ; and 

 how tightly a moss can screw itself up must be seen to be 

 believed. Nothing more unlike the beautiful silky, pinnate 

 stems of Hypnum sericeum can be imagined than the same stems 

 showing their disgust with an east wind. It is obvious that moss 

 collecting in an east wind is more or less of a failure. 



The earlier bryologists relied mainly upon herbarium sheets 

 for the preservation of their specimens, and, while admitting that 

 the herbarium is an essential in systematic work, I incline to the 

 opinion that insufficient attention has been paid to the formation 

 of what may be described as the micro-herbarium. Herbarium 

 sheets at the best can give only the general habit of the plant, 

 and, indeed, in a very large number of species even this is so 

 poorly preserved as to be practically valueless. The specific 

 differences are dependent upon microscopic structure, and either 

 mounted slides or fresh material must be referred to before the 

 species can be named with certainty. Thirty years ago specific 

 distinctions were largely dependent upon general habit and such 

 simple low-power observations as the presence or absence of the 

 so-called " nerve," its length, and the nature of the leaf margin. 

 Hence we find Berkeley contenting himself with the brief remark 

 that an objective of one-third of an inch is the most convenient 

 for examining the leaves, while low powers are sufficient for the 

 determination of genera and species. Since then bryology has 

 become more and more a microscopical study, and Berkeley would 

 probably have been aghast had he been told that almost in his 

 own day specific determination would be to a considerable extent 

 a matter of cell-measurement. Even Braithwaite kept outside 

 the region of the micron. It can be seen that the modern 

 bryologist has of necessity to be at least a fairly competent 

 microscopist, and that the time has come when the carefully 

 displayed sheets of the moss herbarium mean very little to the 

 critical systematist. No bryologist in the present day would care 

 to decide upon the specific names of a large number of our 

 British mosses from an examination in the field, even with the 



