126 S. B. P.\RISH 



A great part of the bottoms is overgrown with thickets of 

 slender willows and cottonwoods, so densely that it is difficult to 

 force one's way through them. Growing in this crowded way, 

 the willows shoot up to a height of 15 to 25 feet, with a base di- 

 ameter of no more than 2 to 10 inches. They are of two species, 

 but, as they were seen only in leaf, their identity is somewhat 

 uncertain. They should be studied at a more favorable season. 

 The smaller is probably Salix exigua Nutt., a species occurring 

 widely in the Colorado desert. The other, readily distinguished 

 at sight when at the sapling state by its rough bark, and eventu- 

 ally becoming a large tree, may be S. Gooddingii Ball. If so, it 

 is hardly distinct from S>. vallicola Britton, which, in turn, might 

 well be left as a variety of S. nigra, as it was considered by Dudley, 

 who first proposed it. Old trees, growing in isolation, have en- 

 tire resemblance to the S. vallicola of the river banks of southern 

 California. Such a specimen may be seen growing on the banks 

 of the Colorado between the railway bridge and the Fort, 



The delta cottonwood, Populus Macdougalii, is abundant along 

 the lower Colorado River and its diffluent streams. The trees in 

 the bottoms near the Fort were apparently of no great age, and 

 no examples were seen exceeding 14 inches in diameter, and an 

 estimated height of 35 feet, but in the lower delta there are 

 trees fully 2 feet in diameter. As it usually grows, in close ar- 

 ray on rich alluvial soil, it is a slender tree. It is conspicuous by 

 reason of its very light gray bark, which on the branches, the 

 larger ones as well as the branchlets, has a shining whiteness. 

 The leaves are small, twice as wide as high, truncate at the base, 

 and short-pointed at the apex. The Alamo River derives its 

 name from the abundance of this tree along its intake and upper 

 courses, and by it, and by New River, the delta cottonwood enters 

 Imperial Valley. 



Other than these the arboreal flora of the bottoms is very 

 limited. Near the Indian church there is a single fairly large 

 Cercidium torreyanum, and a few juvenile specunens were seen 

 elsewhere. There is an occasional mesquite, never of full size, 

 and more screw-beans, which hardly exceed the rank of shrubs. 



Large areas of the bottoms are given over to thickets of Atri- 



