38 Plant Life and Evolution 



of the given temperature. Where the root is in 

 the soil an air temperature of 52 can be borne. 



Modifications Due to Temperature. While a 

 suitable temperature is necessary for normal plant 

 growth, the formative effects of different tem- 

 peratures are far less evident than those due to 

 light. Perhaps the most evident manifestations 

 which seem to be due to temperature are the pro- 

 tective devices seen in plants of cold regions, but 

 these same effects may also be produced by defi- 

 ciencies of moisture. The deciduous habit and the 

 development of scale-clad winter buds may be cited 

 as examples of such temperature modifications, but 

 very similar effects may be noted in plants living 

 in regions where there is a marked dry season. 

 Under such conditions many trees shed their leaves 

 in much the same way that they do in colder cli- 

 mates. In California, for example, the native buck- 

 eye casts its leaves during the long dry summer, and 

 develops resting buds quite like the winter buds of 

 the forest trees of Eastern America. 



As an example of the formative effect of tem- 

 perature among the lower plants can be cited the 

 experiments of Brefeld upon one of the toad- 

 stools (Coprinus). In this fungus it was found 

 that the umbrella-shaped fruiting body was 

 formed in light at a temperature of 12, but in 

 darkness its development required 15. So also 

 it has been stated that certain fern spores, which 

 at ordinary temperatures will not germinate at all in 



