208 JOUENAL OF THE KOYAL HOETICULTURAL SOCIETY. 



say, attuned to drought under desert conditions with a competent water- 

 storage system and sluggish vitahty — aerial absorption by the shoot 

 can do more than enable the plant to maintain life'; but it does not 

 bring us nearer the conception of the plant world taking its water from 

 the air. The facts of gardening, of experiment, of plant-structure, 

 emphatically deny the possibility. 



What, now, is physiological drought as distinguished from physical 

 drought ? 



By conditions of physical drought we understand those in which a 

 plant finds the total amount of water in the soil on which it can draw j 

 is small. It is therefore exposed to the danger of being unable to get | 

 needed water, because there is none to get. 



On the other hand, in conditions of physiological drought there is ! 

 an abundance, or at least adequacy of amount, of water in the soil, 

 but through one cause or another, temporary or permanent, the plant 

 cannot take it in freely or even sufficiently to supply the calls of its 

 organization. The plant finds itself in surroundings where there is 

 ''water, water, everywhere, but scarce a drop to drink." The soil, I 

 though wet, is dry to the plant. < 



In using the expression * * physiological drought, ' * I wish to enter 

 this caveat — it describes a state but does not designate a factor. The 

 factors inducing the state are many, and because of this, exception has i 

 been taken to the use of the term as vague and unsatisfactory, as 

 merely indicating the existence of some obstacle to the intake of water 

 by the root. Admitted. But until further research has isolated and 

 assigned to each factor involved in particular cases its relative influence 

 upon root action, and thereby supplied analytical data for a more 1 

 accurate terminology, the use of the term " physiological drought " 

 in relation to gardening is legitimate and may be illuminating especially 

 in bringing out the contrast with the condition of physical drought. 

 Physical drought implies only a negative environmental state — physio- 

 logical drought involves a positive relationship of the organism itself. 

 The distinction appeals to one as valid. Yet we have to confess that J 

 observation in nature as well as experience in the garden appear to 

 teach that the elasticity of constitution — if one may use a term taboG > 

 to many, but one designating a; fact for which no better has been pro- ! 

 posed — of certain individual plants enables them to deal almost as 

 well with the one condition as the other. That is to say, to somej 

 plants, which are more or less attuned to a struggle in the matter ofl 

 intake of water by the roots, the nature of the obstacle that has to 

 be overcome seems to be of less than vital moment. A plant growing 

 in conditions of physiological drought may live in certain other con 

 ditions more nearly akin to those of physical drought. I say morel 

 nearly akin, because in many conditions which we now regard as merely } 

 indicative of physical drought some physiological factor is probably 

 operative. 



Physiological drought may be temporary or permanent. The dis- 

 tinction is an important one for gardeners, because the causation is 



