590 BULLETIN 347 
finds that the outer and internal cork layers, sclerenchyma (bast fibers 
and stone cells), and crystal-containing cells are not in any way affected. 
All tissues composed of cells having more or less pure cellulose cell walls 
are destroyed (except medullary rays). The collenchyma and the thin- 
walled parenchyma of the primary cortex, the parenchyma of the peri- 
cycle, the sieve tubes and the phloem parenchyma of the bast zone, and 
the fascicular cambium, are enumerated as the tissues that are in most 
cases wholly destroyed and replaced by the fans of mycelium. It was 
found that cellulose cell walls became partially lignified in proximity to 
the advancing edge of the mycelium fan. The degree of lignification, 
however, is not sufficient to furnish immunity of the tissues to the action of 
the fungus, as seems to be the case with the more completely lignified tissues, 
such as the sclerenchyma. The cells of the medullary rays in the bast 
zone are partial y lignified, but the cells are not individually affected or 
broken. There is an increase in the number of medullary ray cells, due 
probably to a stimulating action by the fungus. The original cells divide 
and redivide until great masses of new cells are formed, so that there is 
a crowding of the phloem tissues and a radial and tangential separating of 
the segments of the bast zones. This is the histologic change, evidently, 
which accounts for the slight, and at times pronounced, hypertrophy 
of the cankered area. The destruction of the various tissues of the bark 
is explained on the basis that the cells are broken and destroyed by the 
mechanical action of the advancing mats of mycelium. Since these are 
the only tissues affected to any extent, the fungus must utilize some of 
the material for food. Whether or not enzymic activity precedes or 
follows the apparent mechanical destruction of the tissue was not deter- 
mined. Until the enzymes and the toxins of the fungus are studied, the 
actual biologic relation of the host and the parasite cannot be accurately 
determined. 
CULTURAL STUDIES 
Media 
Endothia parasitica grows luxuriantly on a wide range of culture media. 
The writers, as well as other investigators, have grown it on sterilized 
twigs of many forest trees, on roots, and on bean plugs, carrots, potatoes, 
sweet potatoes, bread, corn meal, oatmeal, rice, sugar solutions, bouillon, 
various synthetic media, and a large number of agar media. In fact, 
in the saprophytic condition the fungus seems to be almost omnivorous. 
Isolation 
The fungus is most readily isolated by removing, under sterile conditions, 
a small piece of the diseased tissue of the inner bark, especially in the 
