clawson: anatomy of janusia. 193 



wood fibers, except that they have bordered pits, while the 

 wood fibers have plain pits. In this plant this is the only dis- 

 tinguishing feature between the wood fibers and the fiber 

 tracheids. These fiber tracheids vary in length from .07 mm. 

 to .195 mm. In width they are from .01 mm. to .018 mm. 

 They exceed the wood fibers in number to a considerable ex- 

 tent, but the exact proportion was not determined. Scattered 

 among the tracheids are wood fibers and wood parenchyma. 

 The wood fibers average about .255 mm. in length and .01 mm. 

 in width, having walls of the thickness of .003 mm., in which 

 there are many plain pits (figs. 3, 4, 5, 6 and 7) . 



The wood parenchyma cells average from .22 mm. to .33 mm. 

 in length and .03 mm. in width. These also have plain pits in 

 their secondary thickening (fig. 14). 



A well-defined cambium is not found in Janusia, but the 

 differentiation between the xylem and the phloem is distinct 

 (fig. 11). The phloem occupies a relatively small amount of 

 both the young and old stems (figs. 1, 7 and 2). It forms a 

 continuous ring, except where it is broken by the medullary 

 rays, and has an irregular outline. The cells are small and 

 elongated vertically, with very little if any other difi'erentia- 

 tion, and in these calcium oxalate occurs. Their walls are cel- 

 lulose, and so far as could be determined there were not any 

 sieve tubes. Sections ranging in thickness from seven microns 

 to fifteen microns were examined with different stains, and 

 with the two-thirds, one-sixth, and one-sixteenth objectives, 

 and no sieve tubes were found. 



The arrangement of the pericycle is similar to that of the 

 usual stem. In young stems it is made up of parenchyma 

 cells and bast fibers. The bast fibers are arranged in a dis- 

 continuous ring. They varj' in length from 1.5 mm. to 2.5 mm., 

 and in width from .007 mm. to .03 mm., and have plain pits. 

 In the old stem the pericycle has difl'erentiated palisade cells 

 next to the endodermis, and in these palisade cells chloroplasts 

 are found (fig. 22). In the inner part of the pericycle are the 

 ordinary parenchyma cells and bast fibers. 



The endodermis is well defined and is filled with starch. 

 Outside of the endodermis, clear to the epidermis, are thin- 

 walled parenchyma cells, no collenchyma being present. The 

 epidermis is made up of one row of cells, in which are stomata 

 and pores (fig. 12) . Over these pores are unicellular trichomes. 

 (A discussion of these will be given under the description of 



