378 



RELATION TO ENVIRONMENT. 



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

 lieved that the scales and liairy 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 

 HA 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 shght as to be almost neg- 

 ligil)le. Indeed, a thermometer bulb 

 covered with scales taken from a 

 horse-chestnut Inid warmed up more 

 rapidl}' than a naked one when ex- 

 posed to sunshine. Tlie wool in the 

 liorse-chestnut bud is not for the pur- 

 pose of keeping it warm, but to pro- 

 tect tlie voung shoot from too great 

 trans])iration after the bud opens the 

 following spring. Research has also 

 Bud of European elm in sec- sliowu thai sucli tempering of the 



ti'Hi, 5nr)\vui>^ iiverlappinR ol ^ 



s^^i'^s- heat conditions is not especiallv bene- 



ficial to the plant, as was once thouglit. Xcitlicr can we find the 

 main function in tlie prevention of water from entering tlie Inid. 

 This might l)e accomplished in much sim])ler ways, e\'cn if we 

 could demonstrate the desiraliilit\' of kee]:)ing the water out at all. 

 The true functions of tlie l)U(l-scales are two in mmilicr: 

 Firstlv, llic prc\"cntirin of too great loss of water from the voung 

 and delivalc (larts witliin; and sccondl\-, tlie protection of these 

 same jiarls from mecliaiii(al inillr^•. \\'illioul sonic such jiro- 

 tcction the delicate "\'oiing siruc lures would be l)eaten off b\' the 

 wind, or beionie the food 'or lninu;ry liirds during the long win- 

 ter months. 



Fir. 430 



