8 BOTANICAL GAZETTE [jutv 



and with no air spaces. In this ground tissue are imbedded the 

 two procambial strands of the traces of the second pair of leaves. 



In the middle of the node below, there is to be seen a ring of 

 vascular tissue inclosing an area of rounded parenchymatous cells 

 similar in appearance to the cortical cells surrounding the vascular 

 tissue. The inner layer of the cortex differs from the remaining 

 cortical cells only in being more tightly placed together, thus 

 forming a sheath. There is as yet no thickening of the walls of 

 the cells forming this sheath. 



Immediately below this node, the sheath sinks in between the 

 four bundles, breaks, the ends turn in and form a complete sheath 

 around each of the bundles, inclosing also a small amount of the 

 undifferentiated parenchyma (pith?) on the inner face of each 

 bundle. This condition persists throughout the internode. At the 

 forking of the two opposite side bundles (figs. 24 and 25), the 

 sheath sinks in between the forks, and so forms a complete sheath 

 around each branch. On entering the cotyledonary node, these 

 sheaths break on the inner face of the bundles, open out, the ends 

 of each fuse with those of the adjacent bundles, forming thus a 

 complete, but at first irregular, sheath around the entire central 

 cylinder of the hypocotyl, which sheath continues downward into 

 the root. At places, the bundle sheaths in the basal epicotylar 

 internode show the characteristic Casparian dots on the side walls; 

 this is also true of the sheath around the central cylinder of the 

 hypocotyl and root. At this stage, however, the sheath is extremely 

 irregular, being often of two layers for a short distance, and in 

 most places showing no special endodermal characteristics. 



A cambium has appeared in the bundles from the first pair of 

 leaves, but very little secondary tissue has as yet been formed. 

 In the hypocotyl there is a much interrupted cambium which has 

 formed a little secondary tissue. At a later stage, the cambium 

 forms a complete ring, and so develops a complete ring of secondary 

 vascular tissue. In the root there is now to be found an inter- 

 rupted cambium, which later becomes complete except at the 

 protoxylem poles. The older primary root, therefore, will have 

 two crescent-shaped masses of secondary tissue, the horns of which 

 come together opposite the protoxylem poles. 



