HYDRATURE AND PLANT PRODUCTION 



K. Kreeb 

 Botanisches Institut, Stuttgart-Hohenheim, West Germany 



MEANING OF HYDRATURE 



The term 'hydrature'* was introduced in 193 1 by Walter (193 la). By it he 

 meant the availabiUty of water to plants. In respect to the water economy 

 the important thing is not the quantity of water but its chemical potential. 

 This point has been explained further by Walter in 1955 in a paper written 

 in Enghsh. As an example we can state: If we irrigate pot cultures with 1 1. 

 of water or with i 1. of a i mol NaCl solution, an appreciable difference 

 exists, even if we use same amounts of water in both cases. 



The word hydrature can be used for any system containing water, for 

 instance solutions, soil, humidity of the air, or imbibed materials. Here 

 mainly the hydrature of plants will be considered, because any change in 

 the water factor outside a plant will be reflected in its hydrature. On the 

 other hand, we are able to check the water condition at a certain location by 

 measuring a plant's hydrature. In that case the plant itself is used as an 

 indicator. 



Generally hydrature {hy) can be measured and expressed by the 'relative 

 humidity'. We say (see Walter, 1950, page 66) : 



hy = —.100 = percentage relative humidity 

 Po 



(p = actual water vapour pressure, po= saturation water vapour pressure at 



* 'Hydrature' as a term should not be used interchangeably with 'hydration' as 

 the terms do not have identical meanings. The word hydrature can be compared with 

 'temperature', which means the condition not the quantity of heat. Accordingly, 

 hydrature does not depend on the quantity but on the condition of available water. 

 'Hydration is a chemical and physical term and means the state of being supplied with 

 water. It is the English verb "hydrate" meaning "to add water to", converted to a 

 noun by adding the common suffix "ion". Hydrature is the Greek noun "hydro" 

 (water) plus the Latin termination "ura" or "atura", much used to denote condition 

 of or effect of, as in juncture, aperture, temperature etc. . . . Accordingly there is a clear 

 parallelism in the words "hydrature" and "temperature", particularly as employed in 

 physiology. Temperature is measured in degrees, hydrature in osmotic pressures, . . . 

 but hydration by a water content determination, hence it is entirely different' (written 

 notice from Prof. J. C. Russel, Lincoln, U.S.A.). 



