(424) 
mycelium or heavy layer of the fungus is composed of brown- 
ish septate hyphae which is much thicker in Sercodes than in 
any of the other species. The mycelium is distinctly marked 
into two regions in all forms except Pterospora. The outer 
region is composed of a looser mesh of strands, which sepa- 
rate into single hyphae which pass out into the soil and per- 
haps penetrate to long distances, constituting the absorbing 
organs of the association. ‘The inner layer of the mycelium 
is generally composed of hyphae which run at right angles to 
the axis of the root. The internal branches which penetrate 
between the cells send off hyphae which gain entrance to the 
epidermal cells in all of the species examined, filling them up 
with meshes of threads in Plerospora and Sarcodes and giv- 
ing rise to various enlargements in Monotropa and Hypofpitys. 
In the former simple branching results, but in the latter the 
hyphae expand to form vesicles, *‘sporangioids, and ‘* spo- 
rangioles” which more or less completely fillthe cells. These 
swollen protuberances are perhaps atrophied reproductive 
branches, and they probably serve as organs of interchange 
between the fungus and the seed plant (Plate 12, Figs. 12- 
20). The entrance of a fungus into the epidermal cell is 
first made at the limits of the root cap. The enlargement of 
a hypha to form a vesicle results in a globular body which is 
filled with fine and then coarsely granular contents. Later 
the vesicles become blackish or brownish. The nucleus of 
the invaded cell is usually pushed toward the outer or distal 
end of the cell, and does not become hyperchromatic. It 
disintegrates however, before exfoliation sets in. Protuber- 
ances which might be regarded as rudimentary root-hairs 
were seen by Kamienski but none have come under our notice. 
In certain instances cells invaded by the fungus are seen to 
contain numbers of globular bodies of a diameter of .0032 
mm. which exhibit a distinct spore appearance (Plate 12, 
Fig. 17). The appearance of some of the sporangioids sug- 
gests that they may be altered conidial branches and that 
these bodies are the result of the more perfect development 
of some of them. 
