270 



ELEMENTARY STUDIES IN BOTANY 



and the cortex, but phloem strands alternate with xylem 

 strands around the centre, so that both xylem and phloem 

 are in contact with the cortex. It is evident that the xylem 

 is to receive and conduct the water and salts from the soil, 

 that these substances must pass through the cortex to reach 

 the xylem, and that they must enter the root through the 

 exposed epidermis and its array of root-hairs. 



The soil is a complex chemical, physical, and biological 

 laboratory, where materials are accumulated and put in 



mm I/- " ''' ' * 





FIG. 232. Live-oaks covered with "long moss." 



available form for plants, and where hosts of bacteria and 

 other fungi are working. The physical properties of the soil 

 in receiving and retaining water, the necessity of drainage 

 so that air may circulate through the soil freely, the adhe- 

 sive films of water about the soil particles, the entrance into 

 the roots of water from the films and not from the free water 

 of the soil, are all physical features that must be kept in 

 mind. 



