440 BOTANICAL GAZETTE [JUNE 
Two densely canescent plants are cited particularly as occurring near 
timber line on Mt. Whitney (p. 55). Since the mountains accord- 
ing to this report (pp. 22 and 42) are not so arid as are the lowlands, 
and the soil is generally more moist, all three habitats, therefore, 
are likely to possess considerable soil moisture. However, to draw 
generalizations from a report is unsatisfactory, since so much depends 
on depth of root system, persistence of foliage, etc. Special study 
of individual conditions in the Death Valley is really necessary. 
In the eastern United States, where conditions are mesophytic, 
hairy plants are found mainly on dry exposed gravelly or sandy 
knolls and hills, as for example Verbascum Thapsus, various species 
ef Antennaria, Gnaphalium, Anaphalis, Solidago bicolor, and 5; 
nemoralis. Here drying winds and hot sunshine prevail during the 
day, but at night the air is still and damp. The soil is not excessively 
dry, but the Verbascum, to still further guard against danger, pos- 
sesses.a long tap root which descends to a considerable depth, where 
a sufficient supply of water is assured. A hairy covering, therefore, 
would best meet the needs of such plants. 
_ The most complete account of the occurrence and function of 
hairy coverings seems to be that given by KERNER.? He seems to 
have believed that the hairy covering so frequently on the under side 
of the leaf alone could be of functional importance only when bathed 
with sunlight. To explain this difficulty he showed how when the 
dry winds blow violently the leaves of the side facing the wind all 
become inverted, so that the silvery under surface faces the sun. 
The present experiments show, on the other hand, that the protective 
action of the hair covering the stomate-bearing surface would be 
great in wind without sunshine. The inversion of the leaves is not 
necessary to explain the functioning; indeed, it is doubtful if such 
inversion continues long enough to be of any great importance. The 
more important fact is that the hairs cover the stomate-bearing 
surface rather than the upper surface. 
KERNER says that hairy coverings are especially pronounced in 
the Alps and in the Mediterranean region, but are almost absent 
from the arctic region. He says that the relation between hairy 
coverings and transpiration stands out strikingly in those districts 
_9 KERNER, A., AND OLIVER, F. W., The natural history of plants 1:313- 
