May, 1904.] 
Deciduous Leaves. 
163 
decidedly from the adults, being clay colored, the bands on the 
posterior borders of the terga in the adults being represented by 
paler markings in these immature specimens. By successive 
moultings, they increased in size and after several weeks became 
colored like the adults when kept in the open air or in sunlight. 
Experiments on the young at different stages failed to bring out 
the adult colors until the normal length had been attained. The 
eggs lie over winter and the larvae emerge in the following spring 
as minute white bodies which grow quickly into the young 
described above. 
DECIDUOUS LEAVES. 
John H. Schaffner. 
Plants have alternating periods of rest and activity. In our 
latitude these periods usually correspond to the alternating con- 
ditions of day and night and to the seasons of the year. The 
active growing period usually occurs in the summer or the rainy 
season and the inactive one corresponds to the cold or dry season. 
Wdiere the seasons are so marked as in Ohio one takes it as quite 
natural that there should be a resting period in the winter. But 
mail}" plants pass into a period of rest even if growing in an envi- 
ronment perennially favorable. Thus it is very common for 
complete defoliation to take place in many plants of the tropics. 
It is said that there are nearly two hundred species in Ce}don 
which become leafless at different times of the year. The state- 
ment is made that there is not a month when all the trees are in 
full leaf. It is evident, therefore, that in many cases the period 
of rest and the deciduous habit are independent of climatic condi- 
tions no difference how the character was originally acquired. In 
our own plants the influence of cold is no doubt predominant. 
The injuries of winter are not only due to the direct effect of cold 
upon the protoplasm, but also to the loss of water. Whth the 
approach of autumn, the chdled roots are unable to suppl}- the 
necessarj' amount of water for the transpiration going on above ; 
consequently there is a great advantage in reducing the transpira- 
tion surface by shedding the leaves. Thus we might say that the 
casting of the leaves is an adjustment to a more limited water 
supply. Plants ma}’ of course go into a period of rest without 
shedding their leaves, as in our common Conifers. In mo.st cases, 
however, there is a great change in the bod)? of the plant or some 
of its parts to prepare for the severe conditions. The annuals die 
completely and the only resting period is in the seed. The bien- 
nials usually grow but little after the cold becomes severe. The 
greater number of geophilous plants die to the ground. The 
woody plants and a few herbs have mostly learned to endure the 
