DEOUGHT AND GARDENING. 



211 



supply — that of conservation and that of obtention — and for the first 

 of these it uses the shoot, for the second the root. 



Reviewing the methods of attunement of the shoot, as we know 

 them, adopted by Nature, she seems to say, ** Drought is drought, 

 however caused," and without criticism of obstacles. Water sufficiency 

 is the main concern, and we find therefore shoot adaptations for con- 

 servation are much the same in all forms of drought, whether physical 

 or physiological. 



Take by way of illustration Nature's method of storing water. 

 That means succulence of the stem or leaf portion of the shoot. You 

 find it in Cacti and Aloe — plants of physical drought of deserts ; likewise 

 in plants like Sedum villosum and species of Cakile — plants of physio- 

 logical drought in bogs and on sea-shore. Then the so-called ** cricoid " 

 habit, with its control of water content, gives us plants like so many 

 Compositae^ — of physical drought on arid plains, and the whole heath 

 family — of physiological drought in peat. Or, again, we have the 

 control by woolly coverings of kinds in plants like species of Marru- 

 hium and Laclinocapsa — of physical drought in desert, or in species of 

 Saussurea — of physiological drought on hill-tops, and so forth. 



All these features — classed now in the terminology of botany as 

 " xerophilous " — are no doubt known to you. It strikes one, how- 

 ever, as paradoxical when one first looks at the matter, that we should 

 find the same growth-form in such diverse conditions of nature as 

 are presented by a desert, a peat-bog, a hill-top, and the sea -shore. 

 Without the clue of physiological drought and the knowledge that all 

 these situations are dry to the plant, the presence in them of like 

 growth-forms is a riddle. 



If the attunement of the conservating shoot to conditions of physio- 

 logical drought is of so general a character, attunement ought 

 assuredly to be more definite in the obtaining root. In the root there 

 is no mere garnering of stores and issuing of them under control for 

 requirements of the household. The much more important task of 

 capturing supplies of water and their intake falls to the share of the 

 rcK>t, and for this a- much more specialized mechanism should be 

 required. It is there for our seeking. But it has not yet been well 

 discovered. When it is the gardener will assuredly find guidance 

 through it. 



Where, as in the case of many orchids, the roots are aerial, and 

 readily observable, our knowledge of the special adaptations they 

 present is no less adequate than our knowledge of adaptations in the 

 stem. But perhaps because of the fact that most roots are under- 

 ground, their relationships to the soil have not been investigated yet to 

 the extent they demand. The ordinary text-book description of soil 

 roots gives only a generalized picture derived from comparatively few 

 examples of accommodating plants, and does not at all apply, for 

 example, to a whole series of plants of physiological drought which 

 Jiave no root-hairs and whose method of intake must be entirely 

 different. Every gardener knows of the extraordinary specific variation 



