210 JOUBNAL OF THE POYAL HOKTICULTURAL SOCIETY. 



air. The key to the advantage of plunging is to be found in its lessen- 

 ing the chances of physiological drought. Wooden pots are ideal. 



In nature under our unstable climate we often see the same effect 

 as that which I have just mentioned as attaching to pot culture. A 

 day in early spring with a cold soil and a bright sun often ruins a 

 gardener's prospects in respect of individual plants. The effect pro- 

 duced on them resembles much that of frosting, and is often so 

 described; but the truth is that temporary physiological drought has 

 operated — loss of water from the shoots exposed in the sun has not 

 been compensated by an intake from the cold soil. An appreciation 

 of this relationship suggests the necessary and usual prophylactics in 

 mulching and shading. 



Conditions of permanent physiological drought offer a more difficult 

 problem to the gardener. Here he has to deal not merely with an 

 environm-ent, but with a plant attuned to it. And if the gardener 

 modify the enviroument, ihe plant may not respond — cannot, indeed, 

 beyond a certain limit, because its structural features have been im- 

 pressed by an adaptation. He has therefore to thole the condition and 

 make the best of it, and he can only do this if he understands the 

 conditions and knows his plants. 



In looking at this problem, two things have to be considered — 



(1) The conditions bringing about permanent physiological drought. 



(2) The attunement of the plants to it. 



The causes of physiological drought are so many that I could 

 easily spread myself over them in a longer discourse than time will 

 allow of to-day, and I therefore select for the purpose of illustration 

 that which appears to me to be the one which the gardener has most 

 often to face. Acidity in the soil always means physiological drought. 

 The form of it which most particularly falls within the domain of 

 gardening is that which is impressed by humus in its extreme forms — 

 peat. 



A long history has yet to be written before grading of the acidities 

 of humus and .peat will be possible. Every gardener knows of the 

 variation. Whatever be the result of ultimate analysis, this character 

 rnay be taken as definitely established — peat soil is dry to plants. 

 A plant growing in peat, however wet that be, is in a condition in 

 w^hich it finds difficulty in obtaining its water-supply — is in a state of 

 physiological drought. In Nature the plant always shows that it is 

 so circumstanced more or less. This is an expression of its attune- 

 ment to the condition. It tells the gardener who has the seeing eye. 

 For whilst many plants in nature have accommodated themselves to 

 average conditions in the matter of water, and analysis has not 

 sorted out up to the present time particular adaptations in them, all 

 plants growing in conditions of a water-relationship outside the average 

 — whether above or below — show in their bodies adaptations to this, 

 and it is those below which we have to consider. 



There are two directions in which Nature turns its efforts in the 

 matter of modification of structure in relation to restricted water- ■ 



