5i4 



ZONES AND REGIONS [Pt. Ill, Sect. II 



over, these two most important climatic factors of plant-life usually exhibit 

 a very unfavourable separation in time from one another. The winter 

 temperatures are on many days high enough to render the work of assimi- 

 lation possible — as that requires but little heat 1 — and at this season, during 

 which the soil contains the most moisture, the flow, as well as the further 

 elaboration, of the raw sap is certainly far more active than during the 

 summer drought. During the summer the temperature, indeed, is con- 

 tinuously favourable for assimilation, but the drought opposes it, as it causes 



contraction or closing of the 

 stomata. It would be highly 

 interesting to investigate, of 

 course only in their natural 

 habitats, the rate of assimila- 

 tion of sclerophyllous plants 

 during the different seasons, 

 and during weather as varied 

 as possible, and to determine 

 whether the low temperature 

 of winter or the drought of 

 summer is the more hostile 

 to it. It is highly probable 

 that the annual assimilation 

 of sclerophyllous plants is 

 not greater than that of 

 periodically green woody 

 plants, as these possess not 

 only a more delicate foliage 

 with less protected stomata, 

 but also allow the leaves to 

 function under much more 

 favourable conditions. 



The great use of the ever- 

 green foliage in a climate 

 with winter rain and summer drought is rendered clear by the above 

 remarks. 



Of the other peculiarities of sclerophyllous plants, the great frequency 

 of scaleless buds is readily comprehensible, for the buds require no pro- 

 tection against drought during winter, seeing that they are formed in 

 summer and may therefore dispense with a hard envelope ; the needful 

 protection is afforded by hairs, coatings of resin, and the like. 



J\ Anfj*»<"' 



Fig. 275. Sclerophyllous flora of California. Quercus 

 chrysolepis. Natural size. After Sargent. 



1 Regarding assimilation during winter by sclerophyllous plants in Chili, see Meigen, II, 

 p. 101. 



