1906] WIEGAND—BUDS AND TWIGS IN WINTER 419 
for temperate regions. He points out that old parts often cover the 
new. The blade of the young leaf is often covered by stipules. The 
most critical time is when first exposed, the walls then being thin 
and feebly cutinized, the chlorophyll dilute and easily decomposed. 
The blades after coming out are folded and covered with hair in such 
a way as to diminish transpiration and radiation as well as to reflect 
light. According to Groom the function of mucilage and tannin in 
buds is to help hold the water in the young shoots. 
In this light I think we can see the function of the air and wool 
which gave the negative results in the temperature experiments. 
Water vapor diffuses through air quite slowly unless the air itself 
is in motion. If a layer of substance containing air passages such 
as wool, through which there is almost no circulation, is placed 
around a damp object, the evaporation from the object is very much 
retarded because the air in contact with the water is almost satu- 
rated under certain conditions. 
The horsechestnut wool, therefore, although not functioning 
in the bud would become a most efficient protection against loss 
of water from young shoots after leaving the bud-scales. I think 
this is the purpose of nearly all hairy coverings of young flowers 
and branches, which view is strengthened by the fact that in most 
cases the hair disappears before maturity. The putting up of the 
hair already in the bud insures its presence at the very earliest 
moment when it shall be required. These and other similar obser- 
vations have quite firmly convinced me that the growing out of 
bud-scales and the presence of hair on the young organs is mainly 
for the purpose of retarding transpiration. In some cases they may 
be important also for mechanical support. 
The observations of Griiss in regard to death at temperatures 
slightly below the freezing point I think can be explained in this 
way. When tissues freeze the water enters the intercellular spaces 
and can from there escape more easily to the outer air. If, however, 
hair or scales were present, not so much water would escape while 
the tissue was frozen, and a lower temperature might be necessary 
to cause fatal loss of water. In the case where —5° R. caused death 
While —4° R. did not, it is possible that freezing just began at that 
point which is near the over-cooling point of such tissue. It may 
