355 
and its Mycorhiza . 
starch. In Thismia they continue from the exterior into the 
exocortex with undiminished general calibre. From this layer 
no plastic material can be conducted along and inside the 
hyphae to the dead mediocortical hyphae. On the other 
hand, food can easily be transported along the wide hyphae 
towards the exterior. Plastic material is undoubtedly being 
continuously absorbed from the host by the exocortical 
hyphae, for starch does not appear in the infected cells (though 
it frequently is found in the limiting layer cells, in which the 
bladders still have their dense protoplasmic contents). Hence 
it is safe to assume that the exocortical hyphae act as haustoria 
for the benefit of the hyphae lying in cells outside them. These 
external hyphae, then, derive from the host a considerable 
amount of nutriment, which enables further growth into the 
substratum outside the host. This method of regarding the 
significance of the hyphae of the sheath and exocortex is 
strongly supported by additional facts referring to Thismia. 
As was before stated, the old end of a thallus gradually 
decays. As the parts die the cells lose their turgidity and 
collapse, so that the whole organ, in that region, shrivels to 
a mere thread. In such disintegrating parts proteid contents 
may be seen in the exocortical hyphae, even after the death 
of the cells which entertain them, and subsequent to the 
complete disappearance of the proteid contents of those cells. 
But these hyphae eventually die and their walls become thick 
and glistening. The hyphae of the sheath die still later, and 
in dead parts of the thallus living hyphae may be traced 
continuously from them to the outside of the plant. In these 
dying and dead parts I found numerous cells, particularly 
superficial cells, crowded with fungal spores produced by 
hyphae which could be traced into the deeper layers of the 
sheath, and also were continuous with hyphae ramifying over 
the surface of the organ. These hyphae were indistinguishable 
from the normal mycorhizal hyphae, excepting that they 
did not run straight in a longitudinal or longitudinal-oblique 
direction in the sheath. In spite of the fact that my sections 
showed the two sets of hyphae coming close together, I could 
