SHINN] HIBERNATION AMONG PLANTS AND ANIMALS 105 



Experiment upon organisms has shown that reduction of heat 

 is the prime factor in determining the seasonal torpidity of the 

 form ; this occurs in both land and water life. Yet in very many in- 

 stances seasonal inactivity has occurred through so many ages 

 that it has become firmly implanted in the protoplasm and now 

 is instinctive. It takes place even when specimen is kept in an 

 artificial summer, as many of us have observed in school-room 

 pets; for instance, turtles, crawfishes, and frogs. 



Among animals hibernation, whether it be habitual and in- 

 stinctive or merely a tropism, consummates the year's activity. 

 In the spring the reproductive functions are dominant ; they involve 

 an almost endless series of physiological changes and the appear- 

 ance of latent faculties of mind concerned with parenthood. 

 During summer the spring's activities and faculties abate while 

 growth and sobriety prevail. The provender of spring and early 

 summer is rank and lush, and while it suffices well for daily need, 

 it is not adapted to long storage. 



For plants, spring is a season of rains and waxing sunshine. 

 Growth is rapid and tissues are rich in simple carbohydrates, 

 substances easy of solution, translocation, and temporary storage. 

 At this time a period of intense cold or of unseasonable heat may 

 prove fatal to vegetation, owing to the instability of material. 



The waning summer is a period of dry heat ; tissues harden and 

 form more enduring compounds. Deposition of cellulose or the 

 withdrawal of sap from new bark effects the formation of a thick- 

 ened corky layer. There is less growth, less rapid translocation of 

 material, until by the time frost sets nightly along the hillsides 

 the plant world is ready for the long winter sleep, its hibernation. 

 Spring flowers are fully formed but safe from rain and wind under 

 waxen scale, or snug and warm in their feather bed, a chaffy bud. 



Seed coats are heavy and even nut-hard. Carbohydrates are 

 mostly cellulose, starch, the glycogen of fungi and the inulin of 

 Compositae ; they may be some form of sugar : fruit sugar (fructose) 

 of fruit and bulb and cane sugar (sacchrose) of beet and cane 

 are most abundant. These carbohydrates are almost insoluble 

 and of high complexity. The fragrant, slightly soluble, volatile 

 oils of spring have been oxidized into odorless and insoluble 

 fixed oils and waxes, most abundant in external parts. They 

 serve as storage material or they prevent evaporation from 

 within or absorption from without. Their complexity of chemical 



