THE AIR 21 



particles of the soil shall be in a state of fine pulverization, whereby its power 

 of retaining moisture is greatly increased. Prof. King, in his work on the 

 soil, illustrated this in the following way : 



A marble, dipped in water, will retain around it a film of water. If it 

 is broken in two there will be an increase of surface to hold a film of water, 

 and if it is pulverized, there will be a marvellous increase in the number of 

 particles, each having a film of water around it. 



These root hairs are produced on a short part of the rootlet just back of 

 the tip as fast as the tip is projected into the soil, and as the root back of them 

 grows older, and the cell walls thicken, the root hairs die off, and that part of 

 the root remains simply as a conduit for the water the root hairs are gathering 

 beyond. 



In this way, the root hairs are being continually formed in fresh soil and 

 are foraging in new pastures. It should be easy then to understand that 

 where a little fertilizer or manure is placed only in the hill, the roots soon get 

 beyond it, and the feeding organs, the root hairs, are hunting for food in 

 poorer soil. 



But the root tip itself is one of the most admirably contrived parts of the 

 whole plant. The extreme point of every rootlet is a little older than the part 

 just behind it. In other words, the actual growing tip of the rootlet is a 

 group of young forming cells under the protection of a root cap. At this 

 growing point new cells are formed to continue the elongation of the root, 

 and to add to the structure of the root cap from beneath, so that the root cap 

 is always being renewed from behind, as it is pushed through the soil by the 

 elongation of the root behind it, and protects the young forming cells beneath 

 it. It is easy to see that this is an admirable provision for the protection of 

 the point of growth. In the older botanical works, it was stated that the ex- 

 treme tips of the roots were what they called "spongioles," and it was supposed 

 that the work of absorption was carried on by the "spongioles." Having now- 

 adays better microscopes, we have learned that there are no "spongioles" at 

 all, but that the protecting root cap goes ever ahead of the advancing rootlet 

 to search out the way, and to guide the root into fresh food. There seems to 

 be a sort of dull sensitiveness in the root cap, by which it is in a measure en- 

 abled to choose its way among the particles of the soil. The roots branch in 

 an irregular sort of a manner, and not after the regularity of the branches 

 above the ground, each branch coming out from the central core of the rootlet, 

 and carrying with it a portion of the outer bark as its first root cap, and then 

 the branches form root hairs just as the main rootlets do. 



The root hairs seem to have tke power, by some sort of secretion, to 

 attach themselves firmly to the particles of the soil and suck moisture from 



