164 STRUCTURAL BOTANY 



their xylem is small, for there is no active water* 

 current to be conducted. 



To sum up : while the foliage-leaves are adapted to 

 the functions of assimilation and transpiration, the 

 scale-leaves of the bulb have only the work of storing 

 up the food which has been formed elsewhere. 



c. Root 



The main root, as we have already seen, only lasts 

 for a short time, though it grows to a considerable 

 length. After the seedling stage is past, the plant 

 has adventitious roots only. Indeed, as seedling 

 Lilies are not common in our gardens, the only roots 

 which we generally see on these plants are adventi- 

 tious ones. They usually arise from near the base of 

 the stem, below the bulb-scales (see Fig. 54, r). They 

 are somewhat sparingly branched. The roots are of 

 large size, and very favourable for investigation. The 

 general structure follows the same lines as that of 

 dicotyledonous roots, but there is this difference: a 

 root of the Lily, like that of nearly all Monocotyledons, 

 has no secondary growth in thickness, but has to 

 depend entirely on its primary tissues ; the latter are 

 accordingly much more highly developed than is 

 necessary in a dicotyledonous root, where there is 

 a cambium ready to make good the deficiencies of the 

 original structure. 



The root of a Lily is traversed by a large central 

 cylinder, which includes a great many distinct bundles 

 of wood and bast, often as many as a dozen of each 

 (see Fig. 64). They are arranged alternately all 



