Double Adaptations 443 



come as small as on the Alps. Continuous elec- 

 tric light had very curious effects; the plants 

 became etiolated, as if growing in darkness, 

 with the exception that they assumed a deep 

 green tinge. They showed more analogy with 

 the arctic than with the alpine type. 



The influence of the soil often produces 

 changes similar to that of climate. This was 

 shown by the above cited experiments of Na- 

 geli with the hawkweeds, and may easily be 

 controlled in other cases. The ground-honey- 

 •suckle or Lotus corniculatus grows in Holland 

 partly on the dry and sandy soil of the dunes, 

 and occasionally in meadows. It is small and 

 dense in the first case, with orange and often 

 very darkly colored petals, while it is loose and 

 green in the meadows, with yellower flowers. 

 Numerous analogous cases might be given. On 

 mountain slopes in South Africa, and especial- 

 ly in Natal, a species of composite is found, 

 which has been introduced into culture and is 

 used as a hanging plant. It is called Othonna 

 crassifolia and has fleshy, nearly cylindrical 

 leaves, and exactlv mimics some of the crassu- 

 laceous species. On dry soil the leaves become 

 shorter and thicker and assume a reddisli 

 tinge, the stems remain short and woody and 

 bear their leaves in dense rosettes. On moist 

 and rich garden-soil this aspect becomes 



