SHELDON: KOEBERLINIA SPINOSA. 101 



lecting in the midst of the rainy season of 1908. (See figs. 5 

 and 6, plate XX.) These pitted vessels, often with ragged 

 inner thickenings (fig. 6), are found from the spiral vessels 

 next the pith to the latest growth. They are also found in the 

 young thorn which bears the flowers. The end of this division 

 of the tracheal tube is often very much elongated and gradu- 

 ally tapering (figs. 3, 4, 9). Sometimes the long tapering is 

 omitted and we have a peculiar cell ending as in figures 6a 

 and 7. These elements sometimes taper at both ends, but fre- 

 quently and abruptly in horizontal base. (Fig. 3.) 



Besides the tube elements just described, there are the more 

 or less rectangular tracheids that join their neighbors above or 

 below by horizontal or oblique walls. (Fig. 13.) 



No means to be had will give an exact account of the age of 

 the stem. This is true of most of the perennials of the desert, 

 we believe. Upon projecting upon the screen by means of the 

 lantern, a cross section of the older stem showed traces of five 

 or six seasons' growth, a slight increase in the size and number 

 of the vessels being noticeable in each successive yearly growth 

 as well as a somewhat greater compactness of growth in the 

 wood itself. Probably for the year 1907 a new set of vessels 

 has been formed. (Fig. 1, plate XVIII.) Outside of these is a 

 second set of larger and unquestionably new water vessels laid 

 down at the beginning of the rainy season of 1908. The width 

 of an annual ring varies somewhat, but on the whole has an 

 average of about 0.2 mm. The entire radial measurement of 

 the wood from pith to phloem is about 1.5 mm. This would 

 make the stem about seven and a half years old. 



The Phloem region shows the usual storage of nitrogenous 

 materials in the sieve and companion cell portion and in the 

 parenchyma. The elements of the sieve vessels are rather long 

 (see table) and full of fine granular material. The sieve plates 

 are heavy, with very minute perforations on the sides. The 

 phloem parenchyma in my material occurs in a series of five 

 parts, each being about three cells wide. (Fig. 1, plate XXI.) 



The stone cells and bast make a hard, rigid cylinder around 

 this more delicate portion, the stone cells occurring between the 

 bundles of bast and extending around them. 



The sclerenchymatous or stone cells are of various shapes : 

 some are squarish, some oblong, and some so elongated as to be 

 confused with the bast as far as shape goes, but possessing 

 the deeply pitted characteristic of the stone cell. This zone 



