73. BOTANICAL GAZETTE [SEPTEMBER 
In a series of forcing experiments, twigs of box elder and of 
several species of maples were placed in the hothouse at intervals 
throughout the winter. All were subjected to uniformly favorable 
conditions for development. The box elder buds opened in about 
one-half the time required by the maples. The same quick response 
is noticeable in the box elder in the first warm days of early spring. 
By thus utilizing the maximum length of the growing season, the 
box elder is able to make its remarkably rapid growth. .This 
again is particularly true of the male trees. 
Brilliant autumnal colors are not developed by box elder leaves. 
Toward the close of long or dry growing seasons, all but the very 
young leaves turn a dull greenish yellow, but do not fall in any con- 
siderable numbers until after frost, when the trees may be entirely 
stripped in a single day. In many of the characteristics here 
noted, the leaves of the box elder differ strikingly from those of 
the true maples. 
The young twigs of box elder also show marked differences. 
Two types are commonly described. In one of these types the 
twigs are of a pale grayish green color, usually quite slender, and 
with rather short internodes. In the other type the twigs are of a 
maroon color, often covered with a white bloom, stout, and with 
longer internodes. These two forms are said to occur in almost 
equal numbers in the eastern part of the range, while the green type 
predominates in the southern part, and the maroon type in the 
northern part. In the course of these studies, it has been found that 
green twigs are usually developed by female trees, and maroon twigs 
on male trees. However, the color of the twigs, in addition to being 
in a measure a secondary sex character, is subject largely to weather 
conditions, exposure, etc. Thus we find vigorous young shoots 
of both sexes pale grayish green in color when growing in protected 
or poorly lighted situations, while both take on more or less of the 
maroon tint when exposed to full light and severe weather con- 
ditions. Also it is to be noted that the maroon color in all these 
twigs gives place more or less completely to green in the warm days 
of spring. In all probability we have here to do with a phenomenon 
similar to the development of rhodophyll and anthocyanin in 
autumn leaves, in rosette plants in winter, in alpine types, etc. 
