INTRODUCTION. 
of the flowering plants, and also the names and their 
localities of 309 Mosses, which had then been discovered as 
growing in this division of the county. It is a very repre- 
sentative list, and contains excellent notes on their distribu- 
tion in the various zones of elevation, and gives the names 
of the contributors. 
The Scale Mosses or Hepaticae, however, are not included 
in this work, as at that period very few botanists had taken 
up this group. 
The true principles of classification, however much they 
have been amplified and refined upon, were in reality 
expressed by Ray, when he defined ''a nainral system to be 
that which neither brings together dissimilar species nor 
separates those which are nearly allied.'' 
One of the best modern works on the British Urn Mosses 
is " The British Moss Flora," by Dr. R. Braithwaite, F.L.S., 
&c., of London, who is a native of Yorkshire, his birthplace 
being Whitby. These humble plants are arranged, so far as 
present knowledge of them, in a natural arrangement. All 
parts and organs of the plants are taken into account more 
or less, and thus a more comprehensive knowledge of their 
structure is gained by this method, than by arranging them 
in the artificial system of fixing upon the variations in one 
particular organ. Nevertheless, in all arrangements up to 
the present time, some plan has to be adopted which may be 
said to be in a great measure artificial. 
The two main divisions into which the Urn Mosses are 
first divided — -viz.^ the Acrocarpous and Pleurocarpous — must 
be so considered. 
In dealing, however, with an insular flora like that of 
the British Islands, some amount of artificial arrangement 
becomes necessary. The mosses may be really put into two 
great groups as regards their distribution over the Globe— 
the Tropical and Arctic. In the British Islands the mosses, 
in a great measure, belong to the Arctic group, but some 
June, 1905. 
