W * M 

 Jfe 4 I Flora of the Palouse Regio?i 



8 or io, successive overflows, between some of which considerable periods of 

 "liuje must have elapsed, inasmuch as layers of soil supporting a forest-cover- 

 ing were formed. The soil of these hills is a black clay-loam extremely fine 

 and wholly destitute of gritty substance. Its greatest thickness over the 

 basalt is perhaps 50 meters. Owing to its fine clayey nature, it is extremely 

 retentive of moisture, which fact alone enables it to support as dense a plant 

 covering as it does. Springs are of frequent occurrence, but the greater part 

 of the subsoil is perfectly dry two or three meters beneath the surface. 



The Thatuna Hills, Kamiack Butte, Steptoe Butte, and other lower knobs 

 are composed of granite or quartzite and geologically are much older than 

 the basalt which envelopes their bases. They have been well designated 

 "islands of granite in a sea of basalt." Owing to its origin, the soil is much 

 coarser than that of basaltic origin, and is less densely covered with her- 

 baceous vegetation. The flora is strikingly different from that of the Palouse 

 Hills. 



Snake River canyon is simply an immense gorge hewn through the basalt 

 but not to the bottom, as the present bed of the river is still like its bluffs. 

 The soil of these bluffs presents various stages of decomposition from the 

 coarse talus at the foot of the cliffs to some nearly as fine as the characteristic 

 Palouse soil. The canyon at its bottom is scarcely wider than the river, ex- 

 cept at the bends where bars of moderate area have been formed, the soil 

 being partially river-sand of granitic origin and partially wash from the 

 bluffs. At its top the canyon is two to three kilometers wide. Owing mainly 

 to the much higher average temperature of the canyon, main- plants of the 

 semi-arid regions along the Columbia occur here together with others which 

 apparently have followed down the river from the south. The flora there- 

 fore contains many plants not found elsewhere in the area. 



The total flora of the region herein described consists of 14 Pteridophytes, 



9 Gymnosperms, 1 14 Monocotyledons and 526 Dicotyledons. It is very doubt- 

 ful if further exploration will increase these numbers by as much as five per 

 cent. With four exceptions, no plant has been admitted into the Flora un- 

 less authentic specimens were in the College Herbarium. Of these four, 

 there is doubt concerning only one as to whether it actually occurs within 

 the limits or not. 



In preparing this brochure the authors have made free use of ever}- avail- 

 able work that was found at all helpful. 



In nomenclature the aim has been to follow the so-called Kew and Berlin 

 Rules. 



Washington Agricultural College and School of Science, Pullman. 

 May 14th, 1901. 



