294 KANSAS UNIVERSITY SCIENCE BULLETIN. 



with this feature we find (a) abundant stomata and (b) 

 strands of sclerenchyma fibers either in the cortex or con- 

 nected with the fibro-vascular system." While the stem of 

 alfalfa would be classed as herbaceous rather than woody, the 

 above description will be seen to apply to it in most respects. 



The chlorophyll region is bounded on the inside by the 

 groups of bast fibers (fig. 2, Ji) , and by lignified sclerenchyma 

 cells, or thin-walled parenchyma (fig. 6 c) , which border the 

 groups of bast fibers on the sides and occupy the region between 

 the vascular bundles, forming the medullary rays. 



The vascular bundles may now be considered more in detail. 

 At the exterior of each bundle in the pericycle is a layer of 

 cells with thickened walls, these walls being lignified, at least 

 on the side towards the bundle, and classed as stone cells be- 

 cause of the unusual hardening and thickening of the walls 

 (fig. 9, e) . They are considered here because of their intimate 

 association with the vascular bundles. In these stone cells may 

 usually be seen embedded crystals of calcium oxalate. (Fig. 

 9, i.) These crystals are simple in their occurrence, clustered 

 crystals being absent in the Papilionacese. Enlarged crystals 

 are shown in fig. 10. This sheath of stone cells, connected as 

 it is with those about adjoining bundles by cells with lignified 

 walls, is part of an almost continuous sclerenchyma sheath sur- 

 rounding the whole system of vascular bundles. Such scleren- 

 chymatous sheaths are reported by Solereder as occurring in a 

 number of the Papilionacese. 



Immediately inside the crystal-containing sheath just men- 

 tioned may be found, just outside the phloem of each bundle, a 

 tissue of compactly associated thick-walled cells, the bast 

 fibers (fig. 2, h) . They often are arranged in the Papilionacese 

 as here found. The bast fibers are greatly elongated and over- 

 lap at the ends (fig. 11, ./ and k), forming a firm, continuous 

 tissue throughout the length of the stem and extending into 

 the main veins of the leaf. The groups are three or four cells 

 in thickness, as a rule. At the corners they are more numerous 

 (fig. 6, a) than on the sides. They are marked by numerous 

 simple pits (fig. 12, m) . The walls of the fibers are lignified, but 

 not so completely as is the xylem woody tissue. The presence of 

 the simple pits in the fibers is characteristic of the Papiliona- 

 cese. Solereder, quoting from .lannicke on Herbaceous Stems, 

 says that in most members of the genus Trifolium, a near rela- 

 tive of Medicago, the vascular bundles are united by inter- 



