EVOLUTION 967 



apex of inflorescence, which is not uncommon in composites, attains 

 a magnitude and succulence which gives this its main cuhnary 

 value, associated as this is, too, with kindred storage in the sheathing 

 bract-bases. 



In the common sunflower the exuberant vegetation-surplus not 

 only goes to magnificent flowering, but affords seed-stores so large 

 as to become of economic value in various regions ; yet in the common 

 and closely allied "Jerusalem artichoke" (not artichoke, and simply 

 gira-sole) we have the extreme contrast of long-delayed and com- 

 paratively insignificant flowering; since the ample leaf -surplus is 

 here conveyed to subterranean stem-tubers, analogous to potatoes 

 alike in general form and uses, to plant or man alike. 



Such instances might be multiplied; but enough to indicate how 

 variations, at first sight seeming "indefinite", may be rationalised 

 as phases and forms of a serial development. 



But our outline of a theory must end by recognising how close 

 to human life the problem is. Man's knowledge cf the universe, 

 of course, depends upon the country he has had to inhabit; but 

 few are at once so securely favoured by isolation, and hence so 

 simply intelligible, as Egypt. The very first of all the necessities of 

 life is not even food, still less clothing, nor yet night-shelter: it is 

 water to drink; for without this we die, in three days commonly, 

 and with extremest suffering. Lakes are few, springs too often unre- 

 liable : hence proximity to rivers, large or small, or to an enduring 

 well, is the main environmental condition of himian existence, be 

 this settled or wandering. 



So, too, plant-life is necessarily most flourishing in soil best 

 watered; hence richest in fruit or seeds to be gathered, in buds to 

 be picked, and roots more easily howked up from moist sol than 

 on the drier and harder upland. As the plant spreads and sinks 

 its roots for water-supplies, its shoots must also grow tall and 

 strong, were it but to nourish these. And so conversely, the larger 

 and deeper the growth of the root system, the taller the stem, the 

 greater the branching or leaf -wealth such roots can water, and hold 

 firm against winds as well. So arises the broad distribution of plants, 

 still easily observed along and across our valley sections, despite 

 man's interferences — that of herbs preponderant by the water's 

 edge, willows and poplars a little behind, and trees rising along the 

 slopes above. The herbs, of course, are ever working their way up- 

 hill; and there are shrubs and even trees which come down to the 

 water edge, and sometimes with submerged roots, like many willows 

 and alders: still in the main, the form of our plant landscape is 

 determined as above. And as each type of growth is ever pressing 

 to extend its area, their struggle is ever varying the landscape in 

 detail. Moist conditions obviously favour growth, and drier accele- 



