I.] EVOLUTION OF THE ROOV. 43 



thicker and thicker," writes King in his book upon 

 "The Soil," "as its water -holding power increased, as 

 the soluble plant food became more abundant, and as the 

 winds and the rains covered at times with soil portions 

 of the purely superficial and aerial early plants, the days 

 of sunshine between passing showers and the weeks of 

 drought intervening between periods of rain became the 

 occasions for utilizing the moisture which the soil had 

 held back from the sea. These conditions, coupled with 

 the universal tendency of life to make the most of its 

 surrounding's, appear to have induced the evolution of 

 absorbing elongations, which by slow degrees and cen- 

 turies of repetition came to be the true roots of plants as 

 we now know them." Some aquatic flowering plants 

 are, as we have seen, still practically rootless, and they 

 absorb the greater part of their food directly by the 

 foliar parts; but the larger number of the higher plants 

 absorb their mineral food by means of what has come to 

 be a subterranean feeding organ, and the foliar parts 

 have developed into gas -absorbing organs, and they take 

 in water only when forced to do so under stress of cir- 

 cumstances. 



But as a mere feeding organ, the root requires no 

 fibrous structure. It is still a hold -fast or grapple, and 

 its mechanical tissue has developed enormously, along 

 with that of the stem, in order to preserve the plant 

 against the strain of the moving elements and to main- 

 tain its erectness in aerial life. When this self -poised 

 epoch arrives, the vegetable world begins its definite and 

 steady ascent in centrogenic form. Whilst the animal 

 creation leaves its centrogenic arrangement early in its 

 own time -scale, the plant creation assumes such arrange- 

 ment at a comparatively late epoch in its time -scale. 



