86 DEGENERATION [CHAP. 



action of the conditions of life." Nothing of the 

 sort ever occurs in water plants. 



I have given my results of growing the rest- 

 harrow in moist earth, and showed how the 

 spines were hereditary until fresh adaptations 

 had taken place by the plant's response to the 

 changed conditions of life. 



Cactuses and euphorbias of dry regions have 

 not only similar succulent stems, but the 

 leaves are reduced to clusters of spines. These 

 plants, however, have lived so long in their 

 respective regions that when grown in this 

 country they retain their forms, when raised 

 from seed, as Cereus, Echinocactus, Mammilaria, 

 Euphorbia, etc. 



I am not discussing hereditary characters of 

 flowers, but in the desert by Cairo there are 

 scarcely any insects, and all the flowers I could 

 find were much degraded as to their corollas, 

 stamens, etc., but they are all self-fertile. 1 



There are very many plants growing on walls, 

 rocks, dry waste places, etc., which are of a 

 diminutive size, as may be expected ; I mention 

 a few names in a note, 2 which any one familiar 

 with our wild flowers will recognise. Some- 

 times botanists have given as a specific name, 

 depauperata, as indicating their impoverished 



1 " Origin of Plant Structures " (Desert Plants) ; and Journ. Lin. 

 Soc., vol. xxx. p. 257. 



8 Erophila vulgaris, Tesdalia nudicaulis, Arenaria tenuifolia, Poly- 

 carpon tetraphyllum, Microcala (Cicendia) filiformis, Festuca (Poa) 

 rigida, etc., etc. 



