THE CONTENTS OF THE SOIL 



31 



worn away by donudation. — See Sir John Lubbock, "Scenery 9/ 

 StriUerUinil," Chaps. Hi. and iv. 



29*1. Even hard .surfaces of rook often support lichens, 

 mosses, and other humble plants. "The plant is co-partner 

 with the weather in the building of the primal soils. The lichen 

 spreads its thin substance over the nx-k, sending its fibt-rs into 

 the crevices and filling the chinks, 

 as they enlarge, with the decay 

 of its own structure ; and finally 

 the rock is fit for the moss or 

 fern or cr«'eping vine, each new- 

 comer leaving its impress by which 

 some later newcomer may profit. 

 Final'.y the rock is disintegrateil 

 and comminuted, and is ready to 

 be .still further elaborated by corn 

 and ragweed. Nature intends to 

 leave no vacant or bare places. 

 She providently covers the rail- 

 way embankment with quack -grass 

 or willows, and she scatters daisies 

 in the old meadows where the land 

 has grown sick and tin-d of grass." 

 I'nnriplcs 0/ Fruit -(inncing, J7G. 



30a. It is interesting to consider the general rea.sons tor the 

 wolution of the root. Plants were at first aipiatic, and probably 

 absorlK-d foo«I from the water on all their surfaces. They mav 

 not have bi««>n attached to the earth. As tlK-y wore driven into 

 a more or loss terrestrial life by the receding of the waters ami 

 as a result of the struggle for existence, they develoiied parts 

 which penetrated the earth. These parts were probably only 

 hold -fasts at first, as the roots of many seaweeds are at the pres- 

 ent time. But as it became less and less possibU- for the genenil 

 surface of tho plant to absorb food, the hold-fa-st gradually b<'- 

 came a foo<l- gathering or feeding member.— .S<'r Survival of the 

 Cnlih. pp. 41-43. 



.'(0/.. If the pupil has aeceM to ledges of rock on which tr«M<H 



m"'^ 



^ -^ J 



-iac^j^' 



F\g. '.'. 1 no halves oi a rock ton*e<J 

 apart by th«> ifrowih of a irw*. 



