86 BulLKTIX of Wisconsin Natural History Society. Vol. 1, No. 1. 
larger rivers, the Milwaukee, Menomonee and Kinnickinnic, with 
the islands lying in them. Secondly, the numerous small water 
courses, and thirdly, the swampy depressions so common on the 
uplands, especially in the Towai of Wauwatosa. 
In several places along the rivers the willows form dense 
thickets in which the oldest and largest trees and shrubs almost 
invariably stand farthest away from the river bank ; in some 
places, where the river has during recent years shifted its current, 
a regular gradation in the age of the willows can be noticed, from 
the line of comparatively old trees at the landward edge to last 
year's seedlings, dipping their young shoots into the water. These 
willow thickets, or saliccta, are all of recent development^ to judge 
from the size of the composing trees and shrubs. In the case of 
one of them, in the Menomonee Valley, I personally recollect that 
twenty years ago it was but just beginning to form. The most 
conspicuous of these river saliceta are that below Helm's mill, on 
the Milwaukee River, and that which stretches in a somewhat in- 
terrupted line along the Menomonee from the neighborhood of the 
Milwaukee & vSt. Paul Raihvay shops to a little above the Monarch 
quarry. The latter I have studied more thoroughly than I have 
the others, and will treat it somewhat more fully in this place. 
The thing- first to attract one's attention in the Menomonee 
salicctuin is the large number of species composing it. 5^. nigra, 
aiiiygdaloidcs and fluviatilis are found in approximately equal 
numbers ; S. liicida, cordata, bebbiana and (i/^co/or sparingly in 
comparison. But besides these wxU-defined types, there are so 
many intermediate forms, whether varieties or hybrids, that they 
may well drive the taxonomist to despair. Salix Huviatilis is most 
frequent on the islands, and nearest the water's edge; nigra and 
amygdaloides on the mainland and farther landward. (2) 
Willows are not the only trees and shrubs occurring in the 
Menomonee Valley saliceta. There is an occasional dogwood, 
2. It has the appearance as if S. fluviatilis had a tendency to be the first on 
the ground, but was later crowded out by the more vigorous growth of the other 
species, which grow taller and overshadow the fluviatilis. The conditions of these 
islands are peculiar. They are composed of coarse gravel and shingle, coming from 
the calcareous rock of the neighborhood, mixed with more or less sand and finemud. 
They are dry during the summer, but more or less covered with water in winter, and 
occasionally during freshets. The shingle allows the water falling on it to percolate 
almost immediately, and has hardly any power of raising water from the lower 
strata by capillarity. Consequently the islands, notwithstanding the river flows 
all around them, are of exceedingly arid character during the vegetation period of 
plants. This is reflected in the xerophytic character of the species which first colo- 
nize these islands. In the summer of'l899 the most conspicuous plant on these 
shingle flats was the wild mustard, with its very deep tap-root and rough leaves. 
Next in frequency was the sweet clover (Melilotus alba), which reduces transpira- 
tion by having comparatively few and small leaves (at least in the upper portions 
of the plant). I am inclined to think that the narrow leaves of S. fluviatilis are 
likewise a xerophytic adaptation. This species, wherever it occurs, tends to occupy 
situations in which the conditions are very similar to those of the Menomonee Val- 
ley shingle islands. 
