46 



Plant Physiology 



water, or the soil solution. When the plant is removed 

 from the soil, even most carefully, organs smaller than 

 the rootlets are not made evident. 

 There are, nevertheless, numerous 

 minute, simple, and effective struc- 

 tures generally present in abun- 

 dance. These are the root-hairs 

 arising from the surfaces of all 

 young and growing roots. 



If seeds of radish or squash are 

 placed in damp mess or germinated 

 between sheets of moist filter paper, 

 or in any of the germinators sub- 

 sequently described, the root-hairs 

 become evident (Fig. 10). As soon 

 as the root has attained a length of 

 an inch or more there are developed 

 at a short distance, behind the tips 

 a large number of these structures. 

 They arise practically perpendicular 

 to the surface, and a microscopic 

 FIG. 10. Radish seedling, examination indicates that they are 



showing root-hairs. . . . 



simple, siphonaceous cells consisting 



of a rather resistant cell-wall within which" is contained 

 the granular protoplasm and cell-sap. 



When grown in the manner indicated, the root-hairs 

 may be perfectly straight tubes. As they develop in the 

 soil, however, where the numerous sharp soil particles 

 obstruct their growth, they bend about and flatten out 

 against and around these particles, becoming, as a result, 

 contorted or deformed in appearance. It is evident that 



