DROUGHT AND GARDENING. 



207 



ing i? responsible for more failures than all other causes taken collec- 

 tively " is a dictum I read in a recent gardening book. And we all 

 agree. 



The particular aspect of the water-relationships of plants to which 

 I propose to devote the time at my disposal is that which in recent 

 years has come to be known as physiological drought or dryness, a 

 condition as influential upon life as the better-known one of physical 

 drought or dryness. The phenomena in gardening, an explanation of 

 which may be obtained by an appreciation of the meaning of this 

 physiological drought, are familiar to all gardeners — but they are often 

 cited as puzzles. Experience tells me that its point is often missed 

 even by keen lovers of horticulture, and I take the opportunity of this 

 occasion, therefore, to bring it before you. It is a subject that would 

 have been after Dr. Mastees' heart. 



At the outset allow me to say that the starting-point of all discus- 

 sions on the relationship of water to the life of flowering plants must 

 be the bed-rock of gardening practice — that such plants obtain their 

 essential domestic supply, if I may so call it, through their roots. I 

 say this with deliberation. 



The matter is one which scientific botany and horticulture cannot 

 afford to ignore, because there has been of late flirtation with the 

 old and often-expressed irresponsible suggestion that the water-supply 

 of plants is derived by leaves from the atmosphere. A weekly periodi- 

 cal devoted some space to an exposition of the theory. Certainly the 

 briUiant work which has been brought before this Society recently, 

 showing the influence of " hormones " in promoting absorption by the 

 leaves, opens a wide field for research, and tells us that we have yet 

 much to learn of the relationships of the leaves to the atmospheric 

 moisture. But at best the consequence of the influence described 

 is only the operation of a regulator upon the plant-pump, without 

 closure of the outflow. Turgescence is maintained, but the vascular 

 system still works. Yet there are interesting cases showing more 

 than this. 



Thus : we had two pot-plants of Euphorbia riparia of about equal 

 size, one of which, having a peculiar curvature near the apex of the 

 stem, presented a construction conducing to the ready retention of 

 water on its surface. The plants were placed side by side in a plant- 

 house with an atmospheric moisture and temperature for " stove- 

 plants." Neither plant was watered at the root, but a teaspoonful of 

 water was placed two or three times a week on the cupped summit of 

 the plant that showed the convenient receptacle. In course of some 

 months a marked difference between the plants was apparent. The 

 one which had not water placed on its stem gradually wilted and died. 

 The other not only lived, but formed a vigorous continuation-shoot, 

 and after two years, at the conclusion of the period of observation, 

 had more than doubled in size. For its water-supply the plant was 

 •dependent upon water supplied to its stem. 



This shows that m special circumstances — in a plant, that is to 



p 2 



