Of Aphyllon Unifiorum, Gray. 115 
STRUCTURE OF THE STEM. 
In cross section the stem shows an epidermis of small 
flattened cells, thick-walled on the outer side (Plate XIV, 
Fig. 3). Beneath is the cortex, composed of large, rounded 
cells; there are usually from eight to ten layers of these cells, 
although the stems vary considerably in this respect. The 
cortical cells are closely packed with large rounded starch 
grains. Within is a more or less continuous ring of degen- 
erate bundles, widely separated in some places by medullary 
rays. Within the bundle-ring again is the pith, its large 
rounded cells packed with starch grains. 
The bundles are arranged in the usual manner, with exter- 
nal phloem and internal xylem. A reduced bundle-sheath is 
present as a frequently interrupted ring of small rounded cells. 
The phloem consists of elongated elements with granular 
contents, which are sometimes nucleated. As in the root, 
sieve-tubes seem to be entirely absent. The protoxylem con- 
sists of one or two spiral trachee with cells. The secondary 
xylem consists of short pitted-reticulate trachez, strongly 
indurated. A cambium is not generally present, although 
some stems show interrupted lines of small cells which may 
doubtfully be interpreted as cambium. Although the xylem 
elements are fairly numerous in root and stem, it seems prob- 
able that the wood has nothing to do with the conduction of 
nutritive liquids, but serves solely to support and strengthen 
the plant. 
The presence of such quantities of starch in a colorless 
parasitic plant is somewhat perplexing. The starch cannot 
have been brought over from the host as such, since starch 
is insoluble, so that Jeucoplasts must be present, and in con- 
siderable numbers. They are, however, small and difficult to 
make out clearly. Moreover it is puzzling to see such an 
amount of reserve food stored in all parts of a purely annual 
