148 
IOWA ACADEMY OP SCIENCE 
Tlie yellow pine forest lias a wholly different aspect from the 
coniferous forests that clothe the western slope. The trees stand 
far apart, their trunks are relatively stout, their tops broad and 
rounded, their foliage thin. They are clothed with no luxuriant 
growth of mosses and lichens, but the older trunks especially 
have a clean-cut appearance and are of a rich cinnamon color. 
No less conspicuous is the almost total lack of undergrowth of 
every description. One shrub, Arctostapliylos mwmanita, does 
occur here and there, and one herbaceous plant, Horkelm fusca, 
but otherwise the thin sandy soil is covered only by a bed of 
dry pine needles. It is possible that there is a limited amount 
of short-lived spring herbage of which no trace could be seen 
while merely riding through in mid-summer. 
For a long distance we pass no spring or stream, but as we 
draw near to the little town of Sisters we cross an inhgation 
ditch, the water of which is derived from Squaw creek. The 
forest now becomes more open and intermpted. Sagebrush, 
Artemisia triderttata^ and juniper, Jumperus occidentalism be- 
gin to appear, and other species of the open dry regions east 
of the Cascades; we are, in fact, almost before we can realize 
it, in the heart of the Arid Transition zone. Here at Sisters 
we are to remain for a few days to make a brief survey of the 
flora. Let us consider, therefore, a few of the most important 
physical features of the immediate locality where our observa- 
tions are to be made. 
The altitude of Sisters is a little over 1100 meters. It has an 
annual precipitation of 451 mm., of which a large part falls as 
snow. The summer temperature is never extremely high, and 
there are late spring and early autumn frosts; in fact, frosts, 
are common in June. The town, of some four or five hundred, 
is situated on Squaw creek. This is a stream of some size, that 
takes its rise on the eastern slopes of the Three Sisters and flows, 
in a northeasterly direction, to empty into Des Chutes river. 
During the summer practically the whole stream is diverted for 
irrigation. 
The water of Squaw creek furnishes conditions favorable for 
a more varied plant life than is to be found in most localities 
in this part of the state. Though apparently along most of the^ 
stream’s course the arid conditions prevail almost to the edge 
of the stream bed, there are in the neighborhood of Sisters some 
good sized meadows, swampy in places, and very narrow bottom 
