TllK SWEET POTATO. 49 



only, or purple below the attaclimeut of the petioles, 

 or purplish or dark purple all over, or brownish 

 green on exposed places, often darker on the upper 

 or lower side. 



Lenticels abundant. Hairs usually present in 

 young shoots from tuber, persistent or not in the old 

 stem. At every joint roots develop on the two 

 opposite sides of the stem. These roots may mature 

 into tubers, depending on the length of season and 

 tiie variety. 



Stem (Microscopical) : (a) Section through tip 

 (Fig. 13). 



Epidermis beset with numerous gland cells, of 

 which some have much darker contents than the rest, 

 liairs more or less abundant, depending on the 

 variety. Epidermis block-shaped, thin- walled; one 

 or more layers of hypodermis well marked, depend- 

 ing on the variety; cortex loose, with intercellular 

 spaces, containing many well-marked latex canals 

 with usually five, occasionally four or six secreting 

 cells, largest latex canals toward the interior of the 

 cortex; endodermis sharply marked, occasionally 

 with a more or less marked accessory endodermis, 

 depending on the variety, the cells of which are 

 intermediate in length (on longitudinal section) 

 between the short endodermal cells and the long 

 cortex cells. Below endodermis an interrupted ring 

 of very thin-walled pericambium, one to three cells 

 thick; phloem very narrow, or of medium thick- 

 ness, depending on variety, xylem well developed, 

 internal phloem consisting of small isolated patches 

 of dividing cells among pith cells smaller than the 

 rest ; pith of large cells with intercellular spaces and 

 numerous latex canals as in cortex. 



