THE SWEET POTATO. 53 



gtuhI into a cushion on lower surface, where it bends 

 sharplv upwards. Cushion sometimes purplish on 

 green petiole, depending on variety. Base of petiole 

 twines around support more or less, depending on 

 variety. Petiole more or less grooved on upper sur- 

 face, rounded on the lower. Just below the attach- 

 ment of the lamina there are two small papillae, one 

 on the right and one on the left side of the petiole, 

 containing the petiolar nectaries. 



Leaf (Microscopical). Epidermis: Consistmg ot 

 irregularlv shaped, more or less sinuate thin-walled 

 cells (Figs. 1 to 4), convex towards the outer surfaces 

 (Figs. 6 to 9), modified in shape when elongated over 

 Imndle traces (Figs. 1, 2), or radiating from gland 

 cells (Fig. 2), or surrounding base of hairs (Fig. 

 1), sometimes showing peculiar wall striations 



(Figs. 3, 4). 



Stomata very frequently on both surfaces (Figs. 

 1, 3, 4, 5, 6), most abundant on the lower, often 

 showing the successive divisions of surrounding cells 

 and guard cells (Fig. 4), sometimes showing double 

 guaiTl cell formation (Fig. 5); less abundant in 

 modified epidermal cells over bundle areas^(Fig. 1) ; 

 on level with surrounding cells (Figs. 6, 7). 



Gland hairs scattered over both surfaces of leaf 

 (Figs. 1, 3, 6), chiefly the upper, consisting of a 

 plano-convex basal cell, on which rests a sohd 

 ellipsoidal mass of 6-8 elongated cells. The basal 

 cell rests on a somewhat broadened epidermal cell 

 which is usually sunk (Fig. 6). 



Mesoplnfll of 'two or occasionally three layers ot 

 palisade parenchyma (Figs. 5 to 7), with stomatic 

 chambers (Figs. 6 and 7), in which may be very thm- 

 walled cells containing calcium-oxalate crystals. 

 Among both the palisade and loose parenchyma cells 



