STRUCTURE. 33 



two or three times as frequent, but somewhat more slender, and, though 

 of nearly the same actual size, are much smaller in proportion to the size of 

 the canals ; they are few in the root of N. flavo-virens, numerous in N.flava 

 and N. odorata, very plentiful and of massive build in N. marliacea- 

 chromatclla. Transverse sections show that they occur only in angles 

 where three partition walls meet, and 

 their arms project into the three adjoin- 

 ing canals (Fig. 8). 



The canals vary in actual and rela- 

 tive size in the different species, but are 

 always largest at the middle of the 

 medio-cortex and smaller toward exo- 

 and endo-cortex. N. odorata (Fig. 8) 

 has six or seven concentric rings of 

 canals, i. e., that number can be counted 

 along any radius of the root ; they are 

 all quite large and distinct. N. tuberosa 

 has seven to ten rows, very irregularly 

 placed ; the middle and outer ones are 

 approximately circular in outline, those 

 near the endo-cortex are greatly elon- 

 gated radially, and the innermost and 

 outermost ones are scarcely more than 

 large intercellular spaces. N. flava and 

 N. lotus have six or seven rows of 

 rounded and quite regular canals in the 

 main part of the root, becoming irregular 

 in N. lotus near the stem. N. marliacea- 



.. FIG. 9. Contractile root of N. flavo-virens, trans- 



has nine rOWS, arranged verse section ; en.endodermis; h, false epidermis ; 



much as in N. tuberosa; the radial ( - latei 



elongation of the inner canals causes the partition walls in this region to 

 look like radial bead-like strings of cells. N. elegans X zanzibariensis has 

 eight or nine rows of large canals, each of a rounded-hexagonal shape ; 

 N . flavo-virens shows a similar structure in its nutritive roots. 



The cells of the partition walls are nearly square in side view 

 (longitudinal section). The angles of the canals are occupied mostly by 

 rounded-hexagonal cells ; three alternate sides of these face the canals, 

 the other three are joined to the neighboring partition cells. Between 

 two angle-cells is usually a single square or rectangular cell ; but often 



4 



