202 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 



Seeing, then, that water so profoundly affects protoplasmic activity, 

 it behoves us to endeavour to get to know as much as we can of the 

 conditions under which the plants extract it from the soil in which 

 they live. 



Everyone knows how different are the root systems of different 

 plants, and there is a rough correlation between the root system and 

 the kind of soil in which a plant can thrive. The Rose, with its small 

 roots, marsh plants with their feebly developed root branches, are 

 obviously not fitted for light dry soils, whilst the enormously developed 

 roots of many plants of the desert and other analogous situations (from 

 a physiological point of view) further confirm the inference that there 

 exists a real relation between root and soil structure. The matter is, 

 however, complicated by other considerations which often mask these 

 relations, as, for example, when the output of water is lowered in 

 consequence of special structural character in the aerial part of the 

 plant, e.g. reduction of leaf surface, &c. Such plants can thrive with 

 relatively small root systems, whilst others which have to extract much 

 inorganic food from a sandy soil obviously can only colonize such 

 situations if they can produce roots which can penetrate the sub- 

 stratum deeply and widely. 



Individual species differ greatly in their tolerance of intermittent 

 periods of dry conditions, and this is one of the practical difficulties 

 the gardener has to contend with in trying to grow all sorts of physio- 

 logically different plants in a somewhat similar environment. In 

 nature it is otherwise, and this water factor is one of the predominating 

 influences which is effective in producing that well-marked facies of 

 certain types of vegetation which it is the fashion nowadays to call a 

 plant association. A knowledge of the water requirement is one 

 of the elements of successful cultivation, and I will illustrate this by 

 reference to two plants whose behaviour in this connexion I have 

 especially studied. 



Lilium Martagon var. album is a plant many people find difficult 

 to grow well ; hence, presumably, its high price. But by attending to 

 its water requirements it is a far easier and more certaii. plant than 

 L. candidum and many other " easy " lilies. If one is acquainted 

 with L. Martagon in its natural home, say in the Alps, where it is 

 very common, one finds it inhabiting rather dry copses, but with 

 water not very far from the surface. That is to say, the bulb is dry, 

 the rather long roots are bathed in moisture. The common Martagon 

 seems to be not very particular, but the white variety is far more 

 sensitive, at least it is so with me, and I have grown it under very 

 different conditions and on very different soils. The one thing that 

 matters is the distribution of water in the soil, and if this need is satisfied 

 success will certainly follow. 



Another plant is Morisia hypogaea, a Mediterranean cruciferous 

 plant, found especially in Corsica. This species will grow in many 

 situations, but I have only found one type of habitat where it will 

 thrive, and form big hardy plants that flower from December to June, 



