28 FLASHLIGHTS ON NATURE 



the tender of a locomotive serves as fuel for the 

 engine, or that the corn in the bin of a stable- 

 serves as fuel to heat the horse's body. These 

 leaves contain material laid by for burning ; and 

 it is by burning that material up at the proper 

 period that the soldanella manages to melt its 

 way out of the wintry ice-sheet, and so to steal 

 a march upon competing species. 



The process requires explanation, I admit ; let 

 us try to understand it. Everybody knows, ;i- 

 a matter of common experience, that animals are 

 warmer in winter than the air which surrounds 

 them ; warm-blooded animals, that is to say, which 

 form the only class most people trouble about. 

 Not everybody knows, however, that the same 

 thing is more or less true of plants as well- 

 that many plants have the power of evolving 

 heat for themselves in considerable quantities. 

 But this is actually true ; indeed, all growing 

 parts of a stem or young leaf-shoot must neces- 

 sarily be slightly warmer than the air around 

 them. For, when you come to think of it, 

 whence do animals derive their heat ? " From 

 the oxidation of their food," the small boy of 

 the day, crammed full of knowledge, will tell 

 you, glibly. And what do you mean by oxida- 

 tion but very slow burning ? You may take a 

 load of hay, and set a match to it, and it will 

 burn at once quickly, by combining with the 

 oxygen of the air in the open ; or you may, if 

 you choose, give it to a pair of horses to eat 

 instead, and then it will burn up slowly, by 



