INTRODUCTION. 



their leaves in the autumn and appear to remain dormant during the 

 winter. This season of rest cannot, however, be a condition of absolute 

 stagnation, as it is obviously necessary to the healthy survival, and to the 

 early start in growth of the tree in the spring, and probably some physio- 

 logical or chemical action goes on which we cannotirecognize. Otherwise 

 it is difficult to understand the quick response, and often the impatience 

 of all checks, so to speak, which vegetation shows on the first slight 

 increase of temperature in the spring, while remaining insensible to much 

 higher degrees of temperature in the autumn. It is true that a few trees 

 do occasionally make mistakes of this kind, but it is only after an exces- 

 sively hot and dry summer, when a period of enforced rest has occurred 

 in a manner similar to that which takes place in the tropics. 



This condition of rest in vegetables (rather than that commonly called 

 " sleep " in some plants) is probably remotely correlated with sleep in 

 the higher organisms, although that condition is usually associated with 

 the existence of a nervous system. The freshness and joyousness of 

 spring has much in common with the condition of body and mind which 

 results from refreshing sleep, and it would seem to be due to some 

 deeper cause than the mere increase in light and heat from the sun's 

 rays on his return northwards. The season of rest in the arctic regions 

 is much longer, and it emerges more quickly into the period of greatest 

 activity than in ours, while in the tropics it is shorter and is not very 

 clearly differentiated from the period of mere growth. 



The threefold division of the seasons is distinguished among insects by 

 the three stages of their life-history — the perfect insect, the caterpillar, 

 and the chrysalis. Some insects in the perfect form are said to hibernate 

 during the winter, but this is probably only a condition of the survival of 

 a few individuals under favourable conditions of shelter and warmth, as 

 the chrysalis state is the correlative of hibernation in animals. Among 

 birds we find the threefold seasons distinguished by the nesting, matura- 

 tion, by fattening of both young and parent birds, and rest by the 

 migration, or the survival on a limited diet during the winter. 



A similar order exists among animals, but the phases are less regular 

 on account of the more varied conditions under which they live. With 

 animals there is a season of reproduction and growing, and a season of 

 fattening, while the season of rest is one of equipoise between the other two, 

 which sometimes proceeds to a state of suspension of all active movements 

 except respiration in hibernation, the animals subject to this condition 

 surviving by the consumption of the fat accumulated during the preced- 

 ing season. Even in man something similar to the periodic phenomena 

 discoverable in the lower animals exist. They are obscured by the long 

 period over which growth extends ; but if children be studied, who are 

 more closely related to the lower forms than adults, periods of growth of 

 fattening, and of equipose are distinguishable. Some observations made 

 on prisoners by Dr. W. R. Miller show that an increase of weight takes 



