Holm. — On Obolaria virginica. 377 
generally scattered, but a few are connected with each other. 
It is not unusual, however, to observe some groups of leptome 
imbedded in the pith (Fig. 12), thus being separated from 
the hadrome. These isolated leptome-groups are very small, 
and contain only a few narrow, thin-walled cells. The 
hadrome is, as stated above, very strongly developed, and 
the tracheids are so thick-walled and tough that it is difficult 
to make good sections of the stem so as to get the pith and 
inner leptome well preserved for study. The pith is composed 
of thin-walled cells and occupies the entire inner part of the 
stem. 
The root-system has several peculiarities. It consists of a 
relatively small number of fleshy, irregularly thickened, and 
wrinkled roots, which show only a few ramifications and are 
of a light brownish colour. The term ‘ coralloid,’ as used by 
Morison, for these roots is, therefore, very well chosen. The 
roots are almost equally developed, there being no main root. 
In this respect our plant agrees with the Saprophytes, except 
the European species of Monotropa , in which a main root is 
developed. In our examination of the anatomical structure 
of the root we were surprised to find that root-hairs are 
entirely absent. A few of the epidermal cells had become 
elongated into short papilli, a fact that again reminds us of 
the Saprophytes. 
An examination of a transverse section of a young root 
(PI. XIX, Fig. 13) will reveal a thin-walled epidermis; a 
hypoderm of only one stratum ; a broad bark-parenchyma ; 
and a thin-walled endodermis, inside of which a pericambium 
surrounds the mestome-bundles. Two groups of leptome, 
separated from each other by a line of vessels corresponding 
to two separate groups, will also be seen, showing that the 
root is of the diarchic type. At this stage the root shows 
a normal development except that it lacks root-hairs. If an 
older, full-grown root (Fig. 14) is examined, it will be found 
to present a very different aspect. While the structure of 
the epidermis and the hypoderm agree with that of the 
young root, the bark-parenchyma will show a great increase 
