408 BOTANICAL GAZETTE [JUNE 
increase the heat absorption. Therefore, these considerations could 
scarcely have been instrumental in bringing about the existence of 
such structures. 
The idea that bud-scales may protect the bud by warding off 
the hot rays of the sun applies mainly to the tropics. It seems 
to have been first advanced by TrEvuB,?" who cites several cases, 
where in plants exposed to the hot tropical sun delicate young 
tissues were inclosed in enlarged stipular organs or else well-shaded 
by overlapping leaves or by other special structural provisions. 
On the same subject, in 1891 another paper was published by 
Porrer.?? According to this investigator many trees in the tropics 
protect their young leaves and shoots from direct sunlight by means 
of stipules. These organs were removed from a number of buds 
and in every case the leaves from these when mature were deformed 
and abnormal. The sunlight seemed to produce injury by causing 
more water to be evaporated than could be replaced. For this 
reason Artocarpus, the most pronounced type of this class, unlike 
most trees, produced leaves throughout the dry season, probably 
because of the stipular protection. Instead of by stipules some 
tropical plants obtain similar protection by various methods of 
leaf-folding, shading by older leaves, and coating with gum. Is 
there not inaccuracy here in his interpretation? Rather than by 
actually preventing the entrance of heat from the sun, which it seems 
such structures could do only to a slight extent, is it not more proba- 
ble that they function simply by preventing the escape of extra 
moisture vaporized by the intense heat ? 
The relation of bud-scales to the young shoot when the bud is 
opening is discussed under internal moisture relations. Suffice it to 
say that the results reached seem to indicate that even in this case 
the scales do not function beneficially by modifying the heat. 
It has sometimes been thought that the layers of hair and wool 
found in many buds, as for example in the horsechestnut, are for 
the purpose of modifying the heat conditions inside. To obtain 
21 TrEuB, M., Iets over knopbedekking in de tropen. Hand. van. het eerste 
Nederlandsch Natuur- en Geneeskundig Congres. Amsterdam. 1887, p. 139- Ref. 
Bot. Centralb. 35:328. 1888. 
22 PoTTER, M. C., Observations on the protection of buds in the tropics. Jour. 
Linn. Soc. Bot. 28: 343. 1891. 
Oa eal 
