RE i ee Se ee are ot ae al ye 
1906] WIEGAND—BUDS AND TWIGS IN WINTER 413 
nut transpired an appreciable amount in winter at a temperature 
of 13-17° C. and a slight amount also at —10° C. This was true 
in older twigs. The leaf scars transpired more than the periderm. 
The winter buds also lost some water. 
That there is actual loss of water in winter probably every one 
knows. My experiments given below show this very definitely, 
but perhaps few understand that there can be a loss when the tissue 
is frozen as well as when thawed, though less in extent. Water 
may evaporate to a large extent from ice crystals themselves, as 
is shown by the drying of frozen soil, damp clothing, and the frequent 
disappearance of small quantities of snow at temperature below 
the freezing point. In buds not all of the water becomes ice, and 
the remainder is free to evaporate as at a higher temperature. 
The fall of temperature on the approach of winter is always 
accompanied by a decrease in the power of root absorption, and 
it has been shown that, to a certain extent absorption is propor- 
tional to the temperature. In the case of our native plants, the 
decrease must be very considerable when the zero air temperatures 
have chilled the soil to a depth of many feet. A compensating 
decrease in transpiration must occur or otherwise the cells will 
suffer from too small water content. This is mainly accomplished 
by the fall of the leaves, but is greatly aided also by the coverings 
of the bud and the waterproof bark. But so far bud-scales would 
not be a necessity, because very little root absorption would probably 
be sufficient to supply the slight amount of water that could evapo- 
rate from unprotected buds, compared with that necessary to supply 
the leaves. Besides, it has been found that considerable water is 
present in the wood at all times, and in some trees even a larger 
amount than in the summer. The necessary factor, I suspect, 
lies in the decreased osmotic activity and vigor of the young tissue 
itself, During the summer the tendency to transpire is probably, 
a large share of the time, not so great as in the winter and spring 
because of the greater saturation of the air; but there are times 
during the summer when the transpiration is very great indeed. 
The young tissues do not then dry up very readily, so that little 
harm usually results. At this time I imagine the growing cells 
are osmotically very active and more easily draw to themselves 
