PHYSIOLOGICAL DROUGHT. 
5 
with crocks and peat, in which orchids naturally epiphytic are 
grown in gardens, and the trunk of a tree? the answer is obvious: 
they are both physiologically dry to the plant. Again in this case 
the botanically-informed gardener could from the xerophily of 
the plants interpret conditions. 
Rhododendron javanicum. —In nature Rhododendron javani- 
cum furnishes an interesting parallel—epiphytic in virgin-forest 
it is terrestrial on solfatara and on alpine highland in Java. 
Xerophilous Plants Indifferent to Cause of Drought.- —These 
and many analogous cases tell us that when a plant is once adapted 
to conditions of physiological drought, that is to say, possesses 
xerophilous characters, it is not particular about the factors im¬ 
mediately causing the difficulty in water-absorption or the method 
in which it is brought about. 
Temporary Physiological Drought through Cold. —Bright sun¬ 
shine, or prolonged winds, or their combination, in late spring in 
Britain, when the soil though wet is still cold, frequently wreck 
temporarily the hopes of a coming season in the garden. Such 
disaster is often attributed to night-frosts. The real cause is a 
temporary condition of physiological drought checking water- 
supply to the shoots. The botanically-informed gardener would 
know that this is induced by low temperature of the soil. 
Pot-cultivation Tends to Physiological Drought. —Further spe¬ 
cific illustration might be multiplied indefinitely, for the whole 
system of cultivation of plants in pots as it is ordinarily practised 
in gardens is one tending to the creation of conditions of physi¬ 
ological drought. 
Gardener may Benefit from Botanical Knowledge. —A proper 
conception of what is implied in physiological drought ought 
therefore to be part of the equipment of every gardener, for it 
will provide him with rational guidance in the regulation of the 
watering of his plants and will enable him to understand why a 
water-supply may vary in its beneficence or its maleficence in 
varying soil-environment and to plants of different water-relation¬ 
ship. This he can arrive at only through botanical knowledge 
from which therefore horticulture can obtain help in regard to a 
fundamental factor in the cultivation of plants. 
