THE SWEET POTATO. 51 



broader patch is sometimes divided in the middle. 

 Crystal cells occasionally occur in unliaiiified xvlem. 

 Xylem cells are not lignified uniformly (as shown by 

 satfranin stain). 



Inside of protoxylem patches there are narrow 

 areas of tissue simiUir to fundamental tissue, with 

 the cells smaller than the cells of the pith. These 

 cells divide the protoxylem from the cambium of 

 the internal phloem. They are probably part of 

 the internal phloem. 



Internal cambium well marked or not, rarely con- 

 tinuous around cross-section, depending on variety. 

 Internal phloem thick or thin, thickest below xylem 

 jDatches with large vessels, depending on the age of 

 the stem and the variety; with or without crystal 

 cells, occasionally enclosing latex canals. 



Occasionally a few secondary xylem cells were 

 found regularly between the protoxylem patches and 

 the internal phloem, giving rise to bundles of reverse 

 orientation. Occasionally the internal phloem and 

 the joining pith cells near such reverse bundles con- 

 tain large fat globules not observed in any other part 

 of other varieties. 



Fundamental tissue of large thin-walled cells with 

 large intercellular spaces and many latex canals, 

 which often show plainly the former plains of divi- 

 sion. Pith cells connected by pore-plates. Crystal 

 cells abundant or not, or absent. Pith cells of 

 normal size and shape, often divided into chambers, 

 each chamber containing a crystal. Occasionally 

 crystals cut off in the corner of a pith cell. Ring 

 fasciation common in some varieties, rare in others. 



(C) Leaf (Macroscopical) : Leaf cordate, hastate, 

 slightly or deeply lobed, or cut (Figs. 74, 72, 70, 

 52, 31, .34). Apex of leaf and lobes obtuse to acute, 



