DEOUGHT AND GARDENING. 



209 



not the same in the two cases, and whilst the former can be obviated, 

 the latter faces us with a problem of organization of the plant. 



As an illustration of the causation of temporary physiological 

 drought, and of the phenomena exhibited by the plant in relation to it, 

 I will take the influence of soil temperature. Lowered temperature — a 

 cold soil — affects the living action of the protoplasm of the root, and 

 water intake is reduced in consequence. As a cause the operation of 

 cold is always temporary, though recurrent in nature. 



The most familiar example of this effect upon plants in nature is 

 that which we see in our climate in leaf-fall, which, to whatever degree 

 it may be a fixed inherited character in many plants, is in origin a 

 consequence of cold soil inducing physiological drought. TO' meet 

 this the plant sheds the organs through which it may lose water, and 

 thus arranges for the conservation of the supply it already has and of 

 the limited supply it may yet obtain. Proof that leaf-fall is an out- 

 come of drought is within the experience of every gardener who has 

 transplanted a large holly or like evergreen. Well watered, as the 

 transplant is sure to be, it throws off leaves. The process is hailed 

 with satisfaction as a mark of vitahty and indication of a successful 

 move. True. But it is in fact a response to the condition of physio- 

 logical drought brought about in this case by an obstacle artificially 

 produced in the plant itself — namely, the diminution by cutting in the 

 number of its roots. There are not enough of them to take in the 

 abundant soil-water in amount sufficient for the organization of the 

 head of foliage of the plant as it existed before transplanting, and 

 the plant now conserves its water-supply by casting the avenues of 

 outgo. 



Temporary physiological drought is always threatening the gardener 

 in his pot culture. Pot culture invites it. Everyone recognizes that 

 there is a loss of water from the surface and sides of the ordinary 

 garden earthenware pot as well as through the plant itself, and dryness 

 requiring correction by addition of water is usually looked at in terms 

 of these factors only as physical — an absence of water. But that is 

 not always the whole story — nor do I imagine it gives us the true 

 picture of the situation which so often Has its outcome in what we 

 call " over- watering." Take a case: a plant stands with its pot 

 exposed to a cold draught or in cold still air and fully sun-exposed. 

 Transpiration proceeds rapidly in the sun. The chilled roots do not 

 absorb adequately. The plant flags — or, it may be, the time for 

 watering comes round. Then we have the mis-use of the watering- 

 can. More water is added to the cold soil already adequately moist, 

 air is driven out, and the thirst trouble of the plant is increased by 

 the further one of threatened suffocation— and this it is which kills. 



Chilling of the root is harmful not directly through the destruction 

 of roots by cold, but indirectly, and exactly in the degree in which 

 it creates physiological drought and hinders thus the intake of water. 

 Glazed pots — I presume introduced with a view to lessening the effect 

 of evaporation from the pot — are yet susceptible to the effects of cold 



