218 PROCEEDINGS OF THE 



their utility — such as their susceptibility of great succulent 

 development under the influence of external stimuli. In the 

 present paper it is proposed to inquire what services they perform 

 to the plant possessing them — what in short is their role in the 

 vegetable system, irrespective of the uses made of them by man. 

 Most people doubtless believe that Potatoes and Carrots were 

 made to be eaten; for the present we must proceed upon the 

 assumption that they were not. The present paper is but an 

 extension of a former subject; the considerations here brought 

 forward having forced themselves on me while trying to solve some 

 of the questions which I then mooted, but could not satisfactorily 

 clear up.* Some of you will, I dare say, remember that in trying 

 to account for the predilection shown by certain plants for the 

 abodes of man, from the fact that the majority of this class of 

 plants bore the impress of a desert flora, I was led to infer that this 

 peculiarity was due to the indirect effects of man's operations on 

 the soil and climate, tending to render these drier. 



I pointed out, further, that plants of a succulent habit were 

 characteristic of regions which were subject to frequent drought, 

 and illustrated the superiority of this class of vegetation over 

 grasses for resisting excessive aridity by a reference to Dr. Living- 

 stone's account of the displacement of the grass by ice-plants or 

 succulent-leaved Mesembryanthemums and Crassulas on the Kala- 

 hari Desert during a succession of severe droughts. From this 

 consideration we were led to infer that the peculiar liking of the 

 House-leek for thatched roofs might be due to its inability to 

 withstand a damp climate, and to its finding on a roof the needful 

 dryness and sun exposure. There were one or two well-marked 

 instances, however, which I found difficult to trace satisfactorily 

 to this class, but I ventured to suggest that they might be 

 originally shore-plants. One of these was the Dock (Rumex). The 

 tap-root of this plant, however, I have since come to regard as a 

 true index of its history, unmistakably proving it to be a desert or 

 shore-plant; so that the Dock undoubtedly agrees with those other 

 plants that grow near human habitations in this respect — that it 

 is highly qualified to withstand drought. 



On the authority of Mr. Darwin, many succulent-leaved plants 

 succumb to a damp climate; and this is probably due to the fact 

 that they have on the surface of their leaves comparatively few 

 Trans. Glasgow Soc. Field Naturalists, 1878. 



