36 KANSAS UNIVERSITY SCIENCE BULLETIN. 



mechanically strong, clue to a large amount of well-developed 

 supporting tissue, and an absence of large intercellular spaces. 

 It contains a rather large proportion of conductive tissue. It is 

 interesting to note here that in the publication by W. A. Cannon 

 (2) on "Water Conducting Tissue of Some Desert Plants," he 

 cites an experiment in which irrigated plants were poorer in 

 conductive tissue than stems of the same diameter from non- 

 irrigated plants. 



Each stem bears a head of flowers, and a cross section at the 

 base of the head shows a collenchyma zone fifteen to twenty 

 cells deep. The collenchyma contains relatively large resin 

 ducts .045 mm. in diameter. The resin glands are more numer- 

 ous at the base of the flower than lower down on the stem. 



The pith, comprising 20.3 per cent of the stem cross section, 

 is composed of parenchymatous cells with comparatively thin 

 and delicately pitted cellulose walls. (Fig. 23.) In cross sec- 

 tion the pith cells vary in diameter from .015 to .067 mm. The 

 walls of a layer of pith cells adjacent to the wood zone often be- 

 come lignified. In the mature stem the pith cells are not empty, 

 but contain some protein, a little starch, and numerous clusters 

 of calcium oxalate crystals, made up of long, slender crystals, 

 which give the cluster a spiny appearance. These crystals 

 sometimes occur singly. 



In the pith, and dispersed through the cortex and the 

 wood parenchyma, there occur round to oval vesicles in which 

 are minute globules that are stained a bright red when left 

 for 24 hours in alcannin or in Sudan III. When sections 

 were put into xylene and left 24 hours they did not show this 

 stain reaction with alcannin and Sudan III. After being 

 treated with xylene, the vesicles are present, and appear to be 

 plastids which manufacture and store up oil. 



The tracheal elements are in radial rows separated by rel- 

 atively broad zones of wood fibers and parenchyma. (Fig. 

 22.) The large ducts occur in greater number near the inner 

 part of the wood zone (fig. 26, w). In transverse section the 

 vessels are round to oval in shape. The tracheal tubes and the 

 tracheids have bordered pits, sometimes slightly elongated, 

 but not enough to justify the use of the term scalariform 

 (fig. 29, g), and single, double and triple spiral thickenings 

 occur on the earlier vessels (fig. 29, h) . 



The ducts, the tracheids, the wood fibers, and the ray cells 



