Number 1 
sD-EXS_ 
Volume 8 
The Plant World 
JHaffa^tne of JJopIat IBotaup 
JANUARY, 1905 
PHYSIOLOGICAL DROUGHT IN RELATION TO 
GARDENING.* 
By Isaac Bayley Balfour, F.R.S., 
Professor of Botany in the University of Edinburgh; Queen’s Botanist in 
Scotland; Regius Keeper of the Royal Botanic Garden, Edinburgh. 
Water-relationship of Plants in Nature.— Everyone who has 
to do with the cultivation of a varied collection of plants learns 
by experience that of all the factors of environment more or less 
under control no one demands more attention than that of water- 
supply, and it is a critical one in gardening. That this should 
be, emerges from the phyletic history of the plants we cultivate 
as descendants of primitive marine forms, and from our dominant 
plant-forms being those which have solved satisfactorily the prob¬ 
lem of adequate water-supply in correlation with a land-life, no 
less than from, the fact that the distribution of vegetation at the 
present epoch is primarily conditioned by relationships to water 
—relationships which we now know are not simply physical but 
physiological, conditioned, that is to say, not by the amount of 
water present but by the degree in which it can be absorbed by 
the plant. 
Water-relationship in Horticulture .—As in nature so in horti¬ 
cultural practice this physiological relationship to water is funda¬ 
mental and furnishes the key to many of those paradoxes which 
* Read before the Botanical Society of America, at Philadelphia, De¬ 
cember 29, 1904. 
