JULY, 1902. 
BRUXCKEX — STUDIES IN PLANT DISTRIBUTION. 
165 
are but slightly paler on the lower side. On the other hand, there 
are no distinct glandular warts on the twigs, and the veins are con- 
spicuously reticular on both sides of the leaves, as in B. pumila. 
A form in which just the opposite characters are similarly min- 
gled, that is tall shrubs with pubescent shoots like pumila, arid 
conspicuous glandular warts like glandulosa, occurs in the Me- 
nomonee valley near Milwaukee. 
The salicetum is rapidly encroaching on the grass area, as 
seen by the numerous clumps of young willows noticeable far 
towards the center of the marsh. On the outside, the shrubs are 
encircled by an equally irregular and interrupted belt of tamarack 
forest, varying in width from a few rods to a quarter of a mile. 
Outside of this the ground rises rapidly to the usual rolling up- 
lands of the region. These are clothed with oak forest, which in 
many places is on the point of transition to oak-and'-maple woods ; 
with the basswood conspicuously numerous, (i) 
In a few places the outer belt of tamarack is absent, and the 
salicetum approaches nearly to the foot of the slope. Here there 
is between the hardwood forest and the willow brush a narrow 
belt of mesophytic grassland, on which both forest and brush are 
encroaching. The outposts of the forest are especially Popiilus 
tremuloides, while in these drier portions of the salicetum Salix 
nigra and 6^. amygdaloides are more conspicuous than the species 
mentioned above. There is another characteristic difference in 
the aspect of the salicetum, according to the degree of wetness. 
In the lower places the willows show greater lateral than height 
growth, so that where a clump stands alone in the surrounding 
grass marsh, it assumes a circular form, hke a bowl turned over, 
with the diameter of its ground area greater than the greatest 
height, which is in the center. On comparatively dry ground, 
the height growth is more vigorous than the lateral spread ; the 
individual shoots are fewer in number, and they show much 
greater diameter. vS. nigra and amygdaloides, in such places, 
often assume tree forms. (2) 
1. Near by, a little south of Calho-un station, there is a twenty-acre timber lot 
which is as good a specimen of young maple wood as there is in the region. There 
are comparatively few old trees left, and these are about one-third oak and bass- 
wood, the rest sugar maple. The very dense underwood of large saplings is com- 
posed entirely of maple, except for an admixture of hop hornbeam. Oak saplings 
are entirely absent. The forest floor is formed by drv leaves, with very scanty 
herbage. This wood, however, is surrounded by a belt of oaks, greatly thinned, 
which forms a strange contrast. Here the grass occupies the ground to the ex- 
clusion of almost all other herbs. Clumps of hawthorn give the area almost the 
character of heath. There are no young trees, and the old oaks show signs of les- 
sened vitality. 
In the midst of this belt, by the way, stands a magnificent, broad-crowned- 
specimen of Acer nigra, which is not a common species in this region. 
2. Compare Bruncken. Distribution of Some Trees and Shrubs in the Vicinity 
of Milwaukee. Bull. Wis. Nat. Hist. Soc, Vol. I, page 38. 
