594 



BOTANY OF THE LIVING PLANT 



being hollowed. The larger the stele the deeper the involutions, 

 and even the number of flanges increases with the size of the whole. 

 This is shown in Fig. 449, where all are drawn to the same scale. 

 With differences of detail similar results may be obtained from the 

 xylem in leafy shoots of Lycopodium, in the leafless rhizomes of 

 Psilotum, and again in roots, particularly in those of Monocotyledons 

 where cambial thickening is absent (Fig. 58). The larger the root the 

 more numerous are the flanges of protoxylem (p. 84). Even in the 

 unicellular Alga, Closterium, where there are in each cell two flanged 

 chloroplasts, the number of flanges varies according to the size of 

 the cell in different species. The measurements taken from such 

 varied objects gain in cogency by tabulation, as they are presented 

 below for the leafless rhizomes of Psilotum, the leafy stems of Lyco- 

 podium, the roots of Colocasia, and for optical sections of the cells 

 of Closterium. 



TABLE SHOWING RELATION OF SIZE TO STRUCTURE IN LEAFLESS RHIZOMES. LEAFY 

 SHOOTS. ROOTS. AND IN CELLS OF DESMIDS. 



