462 PLANT DISTRIBUTION 



(Fig. 128) and in some parts of it almost lacking in 

 summer (Figs. 129-130). Obviously, trees which shed 

 their leaves in winter would be ill-suited to this region. 

 The coniferous trees, on the contrary, because they re- 

 tain their leaves for longer than a year are evergreen 

 and so constituted as to take advantage of opportunity 

 to make food at any season. Trees with broad leaves, 



Fia. 127. — The Coniferous Rain-Forest of the Pacific Northwest, 

 in Washington. The heavy rainfall supports a dense forest of large 

 trees. The smaller trunks in the foreground are those of the giant 

 alder. The large striped trunk at the right is giant cedar. There 

 are also Douglas fir, one or two true firs, and the Sitka spruce. 

 (Vestal.) 



shed in winter or during the dry hot summer, are found 

 in this region but only along streams where the water 

 supply in the soil is sufficient to replace that lost from 

 the leaves. Away from the streams the moisture con- 

 tent of the soil is so much less that, in general, deciduous 

 trees are unable to secure a supply adequate to their 

 minimum noerls in summer. The needle-leaved conifers, 

 however, do not lose water so rapidly and find such 

 habitats suitable. Another factor of some consequence 

 in this connection is the poorer soil of this region over 



