100 KANSAS UNIVERSITY SCIENCE BULLETIN. 



can be made in regard to the structure of these desert plants, 

 each one having its own pecuhar way of getting on. 



The pith occupies a sort of triangular area. The cells are 

 comparatively large (see table), are heavily lignified, deeply 

 pitted, stored with starchy material, and possessed of — in al- 

 most every case — a small crystal having the form of the cal- 

 cium oxalate crystal. In the younger flower branch we find 

 cells with thick walls, also, but retaining their rounded shape, 

 pitted, and plentifully surrounded with air spaces. No food 

 material was observed stored in this region. In the older stem 

 elongated pit cells next the trachial tubes are densely filled 

 with material that stains blue with c. z. i. This has a fine 

 granular appearance (fig. 2, plate XX). 



The medullary rays are conspicuously broad in cross section, 

 many being five cells wide. The cells are comparatively large. 

 They have the ordinary cylindrical shape with thick lignified 

 and pitted walls. (Fig§. 3 and 5, plate XIX.) Intercellular 

 spaces are frequent. Most of the cells are full of non-nitrog- 

 enous material, while a few narrow and elongated ones appear 

 adapted for quick conduction. Those between the phloem 

 strands show the characteristic proteid reaction with c, z. i. 

 and have the usual unpitted walls. Crystals are often found in 

 these cells. 



The xylem makes up a great part of the stem. The wood 

 fibers cannot be said to be very numerous. They have the 

 usual shape and are rather short. (See table.) The fiber- 

 tracheids are found quite plentifully and correspond closely to 

 the wood fiber. The bordered pits, however, are very numer- 

 ous, there being at least 200 to a tracheid. (Fig. 15, plate 

 XX.) The pits are small. The spiral tracheids have the single 

 and double spiral threads. These vessels are decidedly small. 

 The tracheids are of three kinds and vary in length and diam- 

 eter. (See table of measurements.) The tracheal tubes have 

 many small bordered pits and have thickenings in ridges in 

 the walls. The whole tube is divided at more or less regular 

 intervals, as from 0.6 to 0.27 mm., by thick rings. Upon in- 

 vestigation these may sometimes be seen to be in the plane of 

 union of neighboring tubes, the walls being so completely 

 fused as to obliterate all trace of joining. It seems that these 

 rings are really the borders of an aperture in the ends of tube 

 elements, occurring in the earliest laying down of the tissue. 

 They were observed in the last vessels laid down before col- 



