BETA VULGARIS 173 



"In each node, then, the cauline bundles flanking the oldest median 

 trace undergo the following changes: A little distance below, or 

 sometimes above the insertion of the leaf each cauline bundle gives 

 off a small branch which becomes a new lateral trace; a little higher 

 up they approach each other and may even temporarily fuse. Upon 

 separation, the left cauline bundle branches once more and the new 

 strand which is segregated becomes a new median trace. . . . The 

 vascular supply of the axillary members is also derived from the cauline 

 bundles a short distance below the node." 



The Leaf. — In transection, the petiole is roughly triangular 

 with a trough-like depression along its adaxial surface, but its 

 basipetal portion is wide and more or less flattened. At the base 

 of the lamina, the petiole broadens out and forms wing-like pro- 

 jections which are continuous with the blade. The number of 

 bundles in the petiole varies depending upon the development of 

 the leaf, and it decreases toward the blade as a result of anastomoses 

 of the smaller ones. The large bundles extend the entire length 

 of the petiole and are reinforced by crescentic strands of mechanical 

 tissue which lie immediately outside the phloem and to a lesser 

 degree adjacent to the xylem. The petiole is further strengthened 

 by zones of collenchyma located just within the epidermis which 

 are so distributed that they form projecting ridges on the abaxial 

 surface of the petiole and a band several cells in width in the hypo- 

 dermal region of the adaxial surface. 



The epidermal cells are somewhat elongated and there are numer- 

 ous stomata except in regions overlying the coUenchymatous 

 strands. The hypodermal cells may contain anthocyanin, and 

 chloroplasts are present in the compact outer layers of parenchyma 

 and to some extent in the more spongy central parenchyma. The 

 bundles are collateral or occasionally half-amphivasal. The 

 phloem consists chiefly of sieve tubes and companion cells with 

 some parenchyma, while the xylem is comprised of primary and 

 secondary vessels with both thin- and thick-walled fibers. 



The epidermal cells of the blade are polygonal in surface view 

 with sinuous walls and the stomata are simple without accessory 

 cells, each pore being surrounded by a pair of guard cells containing 

 several chloroplasts. The stomatal counts which have been 

 recorded indicate a great variation in the absolute number per unit 

 area, probably due to differences in variety and in the condition of 

 the leaf at the time the count was made. Sixteerucounts, made 

 by Artsch wager (i), of leaves^i^^arying size and color gave an 



