1914] GATES—X EROPHILY 447 
It would seem, at first glance, that plants which grow in bogs, 
where there is an obvious physical water supply, would not be 
restricted in its use, but the various xerophytic adaptations argue 
for the conservation of water in the plant. This fact led investi- 
gators to ask why the plants could not make full use of the water 
present. Many answers have been attempted, and it seems quite 
likely that the true answer is a combination of the different reasons 
rather than any one. The problem presents an obvious result 
obtained from a bewildering mass of causes, whose interactions 
are not yet known. 
The ability of peat bog plants to absorb water is limited on 
account of poorly developed, shallow root systems (FRUH and 
SCHROTER 18), low oxygen content of the water (DACHNOWSKI 9 
and HEssELMANN 23), low aeration (TRANSEAU 49, DACHNOWSKI 
to, and FREE 17), root excretions (Livincston, BrirTon, and 
REID 27, and ScHREINER and REED 45, 46), bog toxins (LIVINGSTON 
29 and DACHNOWSKI 9, 10, 11), the necessity of mycorhizal fungi 
in some species, the low temperature of the soil water (KOSAROFF 
25, Fru and Scurérer 18, and especially TRANSEAU 49), and 
biological processes rather than chemical differences in the soil 
(DAcHNowski 12). Much stress cannot be laid upon the acidity- 
of the soil, as has been done by ScuimPER (44), because of the find- 
ings of later investigations. The acidity is very low and differs in 
different bog associations (TRANSEAU 49). That acidity is a neces- 
sary factor in the soil for the growth of trailing arbutus (Epigaea 
repens) and of the blueberry (Vaccinium corymbosum) was most 
admirably demonstrated by CovittE (6, 7), who found that poor 
aeration was usually the real cause of poor growth and not acidity. 
Acidity, however, may be inimical to certain crops. Sampson and 
ALLEN (42) found that, as a rule, some of the common acids acceler- 
ate transpiration, and that weak solutions often produce as marked 
effects as strong ones. 
The water absorbed is conducted up through the stems. A 
study of stem structure would show whether the ericads differ 
essentially from other bog shrubs. In either case the ability to 
conduct water must be adequate, as the plants thrive. From 
the stem the water passes into the leaves, where the largest 
