390 GYMNOSPERMS 



In such rings as have been mentioned, each ring has its xylem and 

 phloem, as in polyxylic cycads. In transverse section, the bundles 

 are long and narrow, with the xylem cells in rather straight rows for 

 about twenty cells back from the tip, where they become very ir- 

 regular in size and arrangement. It is in this irregular region that 

 one might possibly find some record of seasonal changes. It is not 

 easy to recognize growth-rings in woody monocots; in fact, it has 

 been assumed that they do not exist; but they are easily seen in Aloe 

 bainesii, not quite so easily in A.ferox and Yttcca filamenlosa. How- 

 ever, the rings are there, and they are seasonal. 



In the branching inflorescences the bundles are more regular, the 

 transverse section showing rows of xylem usually one cell wide, with 

 thin-walled parenchyma between (fig. 368). The walls of the xylem 

 elements are extremely thick, and, in a bundle like that shown in the 

 figure, more than half of the cells have spiral or annular markings. 

 The protoxylem tracheids of the lower part of the hypocotyl and 

 root are reticulate, and in the leaf, spiral or annular; but all three 

 kinds may be found together. In the secondary wood, the tracheids 

 have bordered pits, often with reticulations between the pits. 



The cells of the phloem are long and narrow, with prominent nu- 

 clei and sieve areas on the ends, and, also, to some extent, on the 

 side walls. 



Long, very thick-walled fibers occur singly or in twos or threes in 

 the pith; they are abundant just outside the phloem, and throughout 

 the cortex they form long, straight bundles, showing ten to twenty 

 or more fibers in transverse section, with a single section showing 

 more than 200 such strands. 



Stomata are rare on the branches of the inflorescences. The outer 

 walls of the epidermal cells are thick, with three easily recognizable 

 layers; the outer, rather thin and, apparently, not cutinized; a mid- 

 dle layer, somewhat cutinized and containing very small crystals of 

 calcium oxalate; and an inner layer of cellulose. 



Dr. Welwitsch, in a letter to Dr. Hooker, said the plant exuded 

 resin like a conifer. There is some exudation, not resin, but more or 

 less mucilaginous, coming from the disorganization of spicular cells, 

 or from lysigenous cavities. 



The tough, leathery leaves reach a thickness of 2 mm. 'IcMr.ata :ire 



