64 MISSOURI BOTANICAL GARDEN. 
side, and looks as if some obstacle had been put in its path, 
and as if by a series of nutations it had endeavored to get 
away from the obstruction. At short intervals new 
branches appear, up to within a few millimeters of the 
root-tip. The branching is irregular, but the majority of the 
branchlets have a direction parallel to each other so that a 
longitudinal and transverse axis of each tubercle can be dis- 
tinguished. If a longitudinal section be made through a 
tubercle some rootlets are cut transversely, but the majority 
in part radially and in part tangentially parallel to the longer 
axis. A complete radial section is impossible because of 
the contorted form of the roots. A section reconstructed 
from a large number of sections is represented on Pl. 56, 
fig. 1. It is to be noted that all roots keep on growing, 
even after giving off branches, so that on one transverse 
plane there are but few young roots (Pl. 55, fig. 10). A 
transverse section shows most of the roots cut across (Pl. 
56, fig. 2). Between the roots the fine filling of fungus 
hyphae is seen, and about one, a darker ring (‘h’) 
indicating that this section has been made near the tip of 
the rootlet. 
The structure of each root is peculiar. On the outside 
is an epidermal layer composed of elongated cells, looking 
much like palisade cells. These give one the impression 
that the root may have endeavored to get rid of the ap- 
pressing fungus by increasing in diameter. Nowhere do 
any fungus threads enter this layer of cells. The hyphae 
lie closely appressed, and seem to adhere to the cell wall, 
but I never saw any of them penetrate it. Inside this 
epidermal layer come two layers of the cortex, the endo- 
dermis and two radial bundles (Pl. 55, fig. 8). There are no 
intercellular spaces, and the cell walls everywhere are very 
thin. The root tip is much simplified. The root cap con- 
sists of but two layers of flat cells (Pl. 55, fig. 9 «c’) 
resembling in this respect the root cap of the mycorhiza. 
The large columnar epidermal cells originate close 
