FOKEST TREES OF THE PACIFIC SLOPE. 251 



OCCURRENCE. 



At lower levels on river bottoms, sand bars, and banks, in sandy, humous, rich soils, 

 where it is Largest ; at higher elevations, In canyon bottoms and gulches, in moist, sandy 

 or gravelly soil, where it Is much smaller. 



Forms holts and limited forests of pun- growth, or occurs in mixture At north, with 

 willows, red and Sitka alders, vine and broadleaf maples, lowland fir, Douglas fir; south- 

 ward, at higher levels, with red and white alders, incense cedar, and occasionally Doug- 

 las fir. 



Climatic Conditions. Not fully determined, climate in region of besl growth is 

 marked by great humidity and precipitation and by moderate temperatures. Beyond 

 Influence of sea and fogs, where the tree is subjected to dry atmosphere and is dependent 

 Upon soil moisture only, growth is smaller. 



TOLERANCE. — Very intolerant of shade throughout life. Very rapid, persistent growth 

 permits it to hold its own in mixture with more tolerant conifers, among which its small 

 crown is carried high into full light. 



REPRODUCTION. — Prolific annual seeder. Seed has a high rate of germination, but very 

 transient vitality. Reproduction good on moist, bare, humous or sandy soils, but very 

 abundant on wet bars. 



Fremont Cottonwood. 

 Populu8 fremontii Watson, 



DISTINGUISHING CHARACTERISTT* B. 



In its native range Fremont Cottonwood is not known as such, but simply 

 as " cottonwood," a name which should be replaced by the more distinctive one 

 coined from the technical name and adopted here. This tree was long supposed 

 to be the same as the big cottonwood i /'. deltoides) of the Prairie and Eastern 

 States, which it very closely resembles in general appearance. Again, until 

 recently, there had been no stable -character found by which to distinguish it 

 from the perplexingly similar cottonwood (P. wislizeni) of western Texas, the 

 Rio Grande Valley, New Mexico, and contiguous Mexican territory. Fremont 

 cottonwood differs from the latter species in the much longer stems of its seed 

 capsules. 



Ordinarily Fremont cottonwood is from 50 to 75 feet high and from li to 2\ 

 feet in diameter ; rarely it is from 80 to 90 feet and 4 or more feet through. The 

 trunks, clear of branches for about half their length, are seldom straight, but 

 are more or less bowed or leaning. Thick limbs and their drooping branchlets 

 form a very wide, round-topped, open crown. The rough, very deeply furrowed, 

 thick bark is externally dark grayish-brown and clear red within: the wide. 

 distinctly cut ridges are connected Irregularly by smaller lateral ridges. Bark 

 of large limbs ami ypung trunks is only slightly seamed and pale ashy brown. 

 Year-old twigs are smooth, pale yellow, yellowish gray as they become older, 

 with shiny greenish buds. Mature leaves (fig. 110) .are smooth throughout, 

 leathery, rather thick, clear yellow-green and shiny, with Hat, yellow steins. 

 In dying, the leaves become a bright lemon yellow. Wood pale, dull brown, 

 considerably heavier than that of other cottonwoods, fine-grained, soft', brittle. 

 not durable, and specially liable to crack badly in seasoning. Much used locally 

 for fuel, but has in. commercial use. 



Fremont cottonwood is of very great service for protecting .and holding the 

 soft shifting banks of bottomland on western streams, where it is the only tree 

 that marks their meandering courses. 



Longevity. — Not fully determined. Appears 1" grow rapidly to maturity 

 and to be short-lived. <>ne tree :;t;i inches i inside of hark i showed an age of 

 only 20 years. Further investigation of this tree's age limits are desirable. 



