200 TRANSACTIONS OF THE 



a large number of plants, as their botanical or even popular 

 names indicate. For example, agrestis, muralis, tectorum, urbica, 

 murinum, parietaria, wallflower, etc., are terms significant of this 

 peculiarity. The same thing is seen, although in a less degree, in 

 the case of those species whose habitat is a stony or dry waste 

 place. The number of such in the British flora is very great; our 

 common thistles, whins, brambles, and scraggy hedge plants 

 generally, belong to this class. The explanation usually given, is, 

 that in the neighbourhood of towns, nitrogenous and calcareous 

 matters abound. To this it may be objected that these materials 

 are useful to vegetation generally, and it is not at the spots where 

 such matters are accumulated that these plants occur in greatest 

 numbers. It is questionable, moreover, whether plants have 

 such a range of choice in the matter of location, since owing to 

 natural competition, it is only fair to suppose that each species 

 has some peculiar adaptation for its usual abode. 



A close study of the more important examples of plants showing 

 this peculiarity, reveals the fact that they usually possess one or 

 more of the following provisions, the aggregate character of which 

 proves unmistakably, that, viewed as a class, such plants bear the 

 impress of a desert flora. 



Table of Provisions enabling a plant to withstand 



1. Drought. 



(a) Succulent leaves; sempervivum, sedum. 



(b) Succulent tap-roots or tubers; dock. 



(c) Hairs; borago, lamiura. 



2. Attacks of animals. 



(a) Stings; nettle. 



(6) Prickles; brier, bramble, thistle. 



(c) Thorns and spines; whin, hawthorn, wild pear tree. 



3. Nocturnal cold. 



Aromatic leaf-glands ; sweet brier. 



4. Sea water. 



Scales, scurf, and bloom; chenopodiura, silene. 



In addition to the foregoing, it is not improbable that incon- 

 spicuous flowers may be advantageous to plants growing near 

 houses, while others may have their chances of cross-fertilisation 



