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 quickh^ into the 3'oung 

 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. 

 Where 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 

 many 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 Ceylon 

 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. With the 

 approach of autumn, the chilled roots are unable to sujDply the 

 necessar}^ 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 most cases, 

 however, there is a great change in the body 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 



