X PREFACE 



complement) which has been widely used in ecological studies for more 

 than 30 years. As is appropriate for an ecological society, there then 

 follows a considerable section devoted to investigations in natural vegeta- 

 tion, ranging from coniferous forest and sub-alpine vegetation, to psam- 

 mophytes and desert plants. Much work in recent years has been directed 

 to the accurate measurement or estimation of transpiration because of its 

 significance to mankind in water conservation and in forecasting catch- 

 ment yields and floods. To the botanist, however, transpiration has greater 

 significance. In the first place it represents a process which dissipates, 

 often with apparent extravagance, the water in the soil on which growth 

 and survival depend. Secondly, the life processes of the plant are related 

 in a complex way to the balance between the demand of the atmosphere 

 for water and the ability of the soil to supply it. From both points of 

 view the success of the plant is related to its abihty to regulate its trans- 

 piration and its potential on the gradient between soil source and air sink. 

 The ultimate concern of studies on water relations is surely to analyse 

 all aspects of the growth, development, reproduction and survival of 

 plants as they are affected by, or as they affect, the potentials, movement 

 and balance of water in the system. Although we are far from fully 

 understanding the responses of plants to water, our ultimate interest in 

 growth and development has been recognized by reserving for the final 

 section investigations on the relation of growth to climate, soil water and 

 the potential of water in the plant. 



The symposium was held at Imperial College, London, by invitation 

 of the Rector and Professor W. O. James f.r.s., from 5 to 8 April, 

 1 96 1. The conveners wish to record here the thanks which were expressed 

 at the closing session to the College authorities and staff, and the many 

 willing and able helpers who contributed so largely to the smooth run- 

 ning of the meeting and the enjoyment of all present. 



A.J. RUTTER 



F.H. Whitehead 



