238 PHYSIOLOGY OF NUTRITION. 



them over the rest of their surface. To these elongated unicel- 

 lular organs the fine elements of the soil cling very closely; the 

 hairs actually coalesce with the particles of earth, as is easily seen 

 under high magnification. The root-hairs are the organs by 

 means of which the absorption of water and mineral substances is 

 especially effected. They withdraw from the soil the dilute food 

 solutions present in it, but farther, by acting in the manner 

 described in 91 on the closely applied elements of the soil, they 

 themselves prepare food solutions for the plants, which at once 

 pass over into the organism. 



If we grow plants of Triticum vulgare for about five weeks 

 in good garden earth, and then carefully take them out of the 

 soil, it is found, after vigorous shaking, that no soil remains cling- 

 ing to the root-tips or to the older parts of the roots, but that the 

 younger regions of the organs behind the growing points do 

 retain it. These younger regions are covered with numerous 

 root-hairs, while the hairs of the older parts of the root have 

 already perished. 1 



Various observers have determined that the appearance of root- 

 hairs on the roots of plants is dependent on a series of external 

 factors, of which moisture must be regarded as the most impor- 

 tant. 2 We grow seedlings of Zea, A vena, Triticum, Pisum, 

 Phaseolus, in fairly moist garden soil, and determine by micro- 

 scopic examination of delicate transverse or longitudinal sections 

 that moderately developed roots have under these conditions 

 produced numerous hairs. We also raise a few plants of the 

 kinds named without putting them into soil, laying the seeds 

 after soaking, or after the commencement of germination, on net- 

 ting stretched over a beaker of water. We place this in a crystal- 

 lising glass containing water, and cover it with a bell-glass, whose 

 rim must dip into the water in the glass. Daring germination 

 we prevent the plants suffering from scarcity of Oxygen by 

 frequently removing the bell-glass. The roots of many plants 

 (Avena, Triticum) thus developing in water, have root-hairs like 

 the roots of plants grown in somewhat moist earth, as I satisfied 

 myself by experiments with Triticum vulgare. According to Fr. 

 Schwarz, the roots of Zea, Pisum, and Phaseolus, on the contrary, 

 do not develop root-hairs when grown in contact with water. I 

 must, however, remark that at least in the case of Zea Mais, 

 I saw numerous root-hairs appear on quite normal and straight 

 main roots which had developed in water. Perhaps the roots of 



