378 



RELATION TO ENVIRONMENT. 



739. Function of the bud-coverings. It is popularly be- 

 lieved that the scales and hairy coverings serve to keep the bud 

 warm. Research, however, shows this 

 to be almost entirely erroneous, and 

 that the thin bud coverings are en- 

 tirely inadequate to keep out the cold 

 of winter. They cannot keep the 

 bud even a degree or two warmer than 

 the outside air, except when the 

 changes are very rapid. Experiment 

 also shows that the modifying effect 

 of the covering when the bud thaws 

 out is so slight as to be almost neg- 

 ligible. Indeed, a thermometer bulb 

 covered with scales taken from a 

 horse-chestnut bud warmed up more 

 rapidly than a naked one when ex- 

 posed to sunshine. The wool in the 

 horse-chestnut bud is not for the pur- 

 pose of keeping^ it warm, but to pro- 

 tect the young shoot from too great 

 transpiration after the bud opens the 

 Fig . 430- following spring. Research has also 



Bud of European elm in sec- shown that such tempering of the 



tion, snowing overlapping of 



scales< heat conditions is not especially bene- 



ficial to the plant, as was once thought. Neither can we find the 

 main function in the prevention of water from entering the bud.. 

 This might be accomplished in much simpler ways, even if we 

 could demonstrate the desirability of keeping the water out at all. 

 The true functions of the bud-scales are two in number: 

 Firstly, the prevention of too great loss of water from the young 

 and delicate parts within; and secondly, the protection of these 

 same parts from mechanical injury. Without some such pro- 

 tection the delicate young structures would be beaten off by the 

 wind, or become the food for hungry birds during the long win- 

 ter months. 



