WILSON: ANATOMY OF ALFALFA. 293 



(fig. 2, ,/) of the vascular bundles; the xylem, as usual, is inside 

 the phloem region. Inside the vascular bundles is the pith 

 (fig. 2, I). 



The cells of the stem epidermis are, in the main, more or 

 less irregular, and elongated somewhat in the direction of the 

 stem axis (fig. 3, g) . Among these cells occur numerous 

 stomata (fig. 3, /;). Alfalfa is especially weW provided with 

 these, the number on the stem being about 300 to the sq. mm. 

 The walls of the guard cells do not show as much cutinization 

 as do those of the ordinary epidermal cells. 



Numerous trichomes also arise from the stem epidermis. 

 Some of these are two-celled glandular structures, with no 

 apparent content (fig. 3. /) ; others seem to contain active pro- 

 toplasts (fig. 4, m) . A third class of hairs, more numerous, 

 are similar to those found upon the leaves (fig. 5) . The glandu- 

 lar hairs occur about 24 to a sq. mm. ; and the elongated hairs 

 are somewhat more numerous. No vital connection has been 

 found between the trichomes and the activities of the plant, 

 although their presence or absence may serve in distinguishing 

 varieties. The glandular type of hairs is not widely distributed 

 among the other genera of the Papilionacese. Of the forms 

 mentioned by Solereder, those of the alfalfa would seem to be 

 "small, club-shaped external glands, composed of few cells 

 and without a distinctly marked stalk." 



Underneath the outer epidermal cells is a layer of cells much 

 like them, except that the outer walls are not cutinized or 

 thickened to so great an extent (fig. 7, n) . The corners of the 

 stem are strengthened by a tissue (fig. 2, g) , extending from 

 the epidermis to the lignified tissue surrounding the corner 

 vascular bundle. This arrangement makes the angles of the 

 stem especially strong and leaves four regions of chlorophyll 

 tissue (fig. 7, o) between the bundles of the bast and the epi- 

 dermis on each side of the ^tem. In these chlorophyll regions 

 there are numerous air spaces between the cells. There are 

 several layers of the chloroplast-bearing cells. The chloro- 

 plasts are of the usual lens-shaped type, peripherally ar- 

 ranged. In this region, rich in protein, the main food value of 

 the alfalfa stem lies. Solereder, in discussing the presence of 

 such chlorophyll regions in the stems of Papilionacese, says : 

 "In many woody species, principally those with reduced leaves, 

 much of the primary cortex is developed as palisade paren- 

 chyma or assimilatory tissue of some other form. Associated 



