ROOTS. 15 



Each of the soil particles has a very thin adherent film of 

 moisture, and this it is that the root-hairs absorb. In this 

 manner the dissolved mineral food is conveyed into plants to 

 be converted into organic (vegetable) matter for building up 

 all their parts. Solid particles are not taken up by the plant. 

 However, the tip of the root-hairs is often acid — as test with 

 litmus paper will demonstrate — and the hairs are therefore 

 capable of dissolving to some extent the mineral particles to 

 which they affix themselves. 



Plaice a number of seeds, as Com or Wheat and Beau or Sunflower 

 (previously soaked in water), on the surface of wet sand in a shallow box 

 or tray — first covering one-half of the area with a thin sheet of white 

 paper. Cover the box with a pane of glass to prevent evaporation. The 

 seeds which germinate on the paper will in two or three days furnish good 

 examples of root-hairs visible to the unaided eye, but seen more satisfac- 

 torily with a pocket lens. The roots of the other seedlings, not prevented 

 from penetrating the soil, when pulled up will have a mass of particles cling- 

 ing to them, some of which can scarcely or not at all be washed off (soak for 

 a few moments and then use a camel' s-hair brush) — showing that the hairs 

 have taken firm hold on the minute mineral particles. 



3. Though granite, limestone and other rock-materials are 

 usually said to be insoluble, yet the rain water, percolating 

 through the soil and there becoming more or less charged 

 with carbon dioxide and alkalies, does slowly dissolve even 

 these refractory mineral matters. While each root-hair ab- 

 sorbs but a tiny drop of this soil-water, the countless myriads 

 combined, take up for the plant a stream that furnishes the 

 food-material required from the soil. That rootlets can dis- 

 integrate mineral matter is shown experimentally by their 

 perceptible corrosion of a piece of polished marble with which 

 they may come in contact. 



Place a small piece of marble, with one face polished, near the bottom of 

 a box or pot of soil. Plant seeds so that the roots of the seedlings will touch 

 and spread over the polished face as they grow. After an interval of time 

 (fifteen to thirty days) remove the piece of marble and see the corroded 

 lines where the roots have been in contact. Euhbing the surface with ver- 

 milion will render the corroded parts more conspicuous. 



4. Since all soils are porous — even the finest clay has space 



