1914] GATES—X EROPHILY 453 
leaves are at least slightly revolute, those of Andromeda and Salix 
candida strongly so. The leaves are usually dark green in color, 
but often reddish at the beginning and close of the vegetative 
season. The abundant presence of cutin in the evergreen ericads as 
an efficient xerophytic adaptation against loss of water at all times, 
but especially in winter, has been brought out by WIEGAND (51). 
A considerable amount of water is transpired by many bog 
plants, and the loss may be as great as or greater than that from 
mesophytic plants of the same vicinity. This suggests that it is 
e€ maximum rate to which the plant may be subjected rather than 
the amount of water lost that is the important consideration. If 
the amount of food material is correlated with the amount of water 
lost, there would have to be considerably more water absorbed in 
the bog habitat, as it is notably deficient in available mineral food 
material (TRANSEAU 49). Plants that normally grow in non-bog 
conditions, as white pine and black spruce, when growing under 
bog conditions are much dwarfed and stunted, and their leaves 
exhibit very pronounced xerophytic modifications, so much so that 
these plants growing in bogs have received specific designation. 
Some plants, as Populus tremuloides and Poa pratensis, that 
may grow in either bog or mesophytic soil, do better in the latter 
situation and always exhibit a pronounced xerophily in the bog 
soil. Some plants demand bog conditions and even then have 
xerophytic modifications, as COVILLE (6) demonstrated in the case 
of the blueberry. 
During the growing season, all of the bog plants have their 
transpiring organs, but the great majority do not retain them during 
the winter. In every case where leaves are retained, their winter 
position is different from their summer one. The winter position is 
usually upright, but in the evergreen conifers the leaves are more 
closely appressed to the twig. The young leaf as it comes out in 
the spring is also upright and remains so at least as long as it is 
tender. The fact that the dark upper surface is innermost when the 
leaves are upright serves to protect it by reducing the amount of 
radiant energy absorbed, which would raise the temperature of the 
mesophyll cells and lead to greater loss of water. The under sur- 
face is already well protected. The upright, upper surface to upper 
