1915] PLOW MAN—BOX ELDER I7I 
were in the majority on more than 32 per cent; while on about 
62 per cent of the trees most of the leaves were 7-foliolate. Two 
trees out of the entire number showed 9-foliolate leaves in greatest 
numbers. No tree bore one type of leaf exclusively, except a very 
few having only the 3-foliolate sort. No 3-foliolate leaves occurred 
on the 7 and g-foliolate trees, neither did the 9-foliolate leaves 
appear on 3 and s5-foliolate trees. The higher number of leaflets, 
as well as the larger and more deeply lobed leaves, occur on suck- 
ers and second growths. In general, the leaflets are more numer- 
ous, larger, and more deeply divided on staminate trees. The two 
g-foliolate trees mentioned above were both staminate trees. 
More than 7 per cent of the leaves studied bore trifoliololate 
basal leaflets, such as are shown in no. 6 of fig. 1. Intermediate 
forms appear in nos. 3, 4, 5, and 7 of the same figure. It was 
impossible to detect any intimate and constant relationship between . 
leaf types and the quality of the soil in which the trees grew. 
Light and shade relations seem to be more effective agents in this 
respect, the higher number of leaflets usually occurring on the more 
brightly lighted trees and parts of trees. The leaves of box elder 
are commonly thicker and of softer texture than are those of true 
maples growing in similar situations. 
An interesting peculiarity of the box elder is its very common 
habit of developing new buds and leaves as long as the growing 
season lasts. In other words, its growth is indeterminate. This 
characteristic seems to be more pronounced in the northern part 
of the range. Here not uncommonly the box elder trees con- 
tinue to develop new leaves at the tips of the twigs until checked 
by the first killing frost. This fact accounts for the diffuse and 
angular habit of the trees in the colder parts of the range, since 
because of this mode of growth the terminal buds are usually killed, 
and the lateral buds carry on the development in the following 
season. Indeterminate growth is much more conspicuous in the 
male trees than in the female, especially in those years when the 
female trees bear a heavy crop of fruit. This in turn explains why 
the female trees are so much more symmetrical in form, and hence 
better suited for artificial planting and cultivation, than are the 
male trees. 
