98 The Vegetation of the Scottish Highlands . 
root-system every growing season, and which needs to get its life 
processes into full swing at the shortest possible notice, cannot 
possibly tap so large an area for salts as an ordinary herbaceous 
plant with a perennial root-system. Also even if it tapped an equal 
area it would need to take in salts much more quickly to make up 
for the shortness of its growth-period. This seems to indicate that 
the aid of a mycorhiza would be particularly valuable, as a more 
effective and much less costly method of obtaining salts, than the 
production of a very elaborate root-system. Dicotyledons have a 
root-epidermis (climacorhizic, type of Van Tieghem) while Mono¬ 
cotyledons are characterised by the absence of such an epidermis 
(liorhizic type). The point upon which I wish to lay stress is that the 
absence of epidermis in the roots may conceivably facilitate the 
entrance of the fungus, and this character (though it may have 
arisen independently, and have been simply utilised in this con¬ 
nexion) might possibly have been evolved in connexion with the 
mycotrophic habit of life. Its retention in such specialised Mono¬ 
cotyledons as the Gramineae, which have become strong transpirers 
and have given up the mycorhiza, would then be explained merely 
as a hereditary trait which has survived, although its original purpose 
is lost. 
A. R. 
THE VEGETATION OF THE SCOTTISH HIGHLANDS'. 
E know of no more interesting and attractive general account 
of the vegetation of a country than the present work by 
Mr. Hardy of University College, Dundee. As its title implies it is 
no more than a sketch of the leading features of the vegetation. 
The writer passes quite lightly over the different plant-formations 
met with, some of which have already been closely studied by 
R. and \V. G. Smith, but his broad general standpoint, and the 
different points of view from which he surveys the vegetation, 
furnish the reader with a most illuminating coup d'ceil. 
1 Esquisse de la geographic et de la vegetation des Highlands 
d’Ecosse, par Marcel Hardy. Paris, 1905. 
