THE SWEET POTATO. 55 



to those already described as occurring on the 

 lamina, but consisting of more cells. That insects 

 may be attracted by these gland areas appears prob- 

 able from the fact that one of the sections contains 

 an insect in the nectary. Fungal hypha^ are com- 

 monly found in these petiolar nectaries. 



Petiole, sectioned one inch from the base (Figs. 11, 

 12) : Great difference in size, dei)ending chiefly on 

 variety; in those with larger diametei- all cells are 

 also proportionately larger, the epidermal cells being 

 increased least. Epidermis shows gland cells as 

 in leaf, may show hair as on leaf, usually larger, and 

 sometimes a peculiar proliferation, which gives the 

 impression of a lenticel. One to two layers of 

 modified chlorophyllous hypodermis are present, 

 and the entire fundamental tissue is enclosed in a 

 sheath of collenchyma from two to five or six cells 

 wide, varying in width with the different parts of 

 the same section, and in corresponding parts of the 

 sections from different varieties. 



Latex canals frequent, irregTilarly distributed 

 throughout pith tissue, secreting cells well or fairly 

 well marked, depending on the variety. 



Arrangement of bundles in petiole typically in five 

 parts, the three central ones enclosed by a common 

 endodermis and 23ericambium, and two upper ones 

 each with its own. Pericambium at times two layers 

 thick. Depending on the varieties, the arrangement 

 of the bundles may be in more than five patches, and 

 instead of three patches of endodermis, there may 

 be four. In all cases small patches of internal 

 phloem are found isolated from the xylem and from 

 each other, among small pith cells interior to the 

 xvlem. 



In some varieties small groups of dividing cells 



