Root Action in Plants. 



147 



179. Structure of Boot Hairs. Boot hairs are extremely 

 thin walled and greatly lengthened single cells, having 

 lengths ranging up to an eighth or quarter of an inch and 



a diameter of ifo of an 

 inch. They stand out 

 about the main root like 

 the pile of velvet, forming 

 a brush-like appearance 

 as shown, in Fig. 44. The 

 object of this form is to 

 secure a large area around 

 which surface tension 

 may force the water in 

 the same way that it does 

 about the soil grains. In- 

 deed root hairs have 

 forms adapted to drawing 

 upon themselves a portion 

 of the water film invest- 

 ing the soil grains. 



180. Relation of Root 

 ! Hairs to Soil Grains. The 

 manner in which root 

 , hairs place themselves 



Fio.45. Apparatus for observing the growth f. ., 



of roots and their relation to soil grains, among the SOll grains IS 

 The sides of the apparatus are two panes , -, 7i j? 



of glass, 1.5 inches apart. clearly shown in the form 



of a diagram in Fig. 46 where h h is a root hair ; e is the 

 main root, 2 a soil granule, and 1 an air space ; while the 

 concentric lines represent the films of capillary moisture 

 which surround both the granules and the root hairs. In 

 Fig. 47 is represented the tip of a young growing root ad- 

 vancing into fresh soil and having five root hairs developed 

 in place among the soil grains ready for work. 



181. Method by which Root Hairs Gather Water. As the 



root hairs force their way through the pore spaces among 

 the soil granules they bring their walls into close touch with 



