26 BULLETIN 380, U. S. DEPARTMENT OF AGRICULTURE. 
the pycnidia in pure culture and made sections of perithecial stro- 
mata growing on bark. 
According to Anderson, the pycnidium originates as a mass of 
densely intertwined hyphe, in the center of which numerous pycno- 
spores are cut off. The crowding of these spores increases the size 
of the pycnidial cavity and crowds the outer hyphx together to form 
a sort of wall. The ostiole is formed in the top by the loosening of 
the hyphe. The stroma always starts as a loose growth of hyphe 
around the pycnidium. It does not precede, but follows the first 
stages in the development of that organ. A fluffy growth of light- 
yellow mycelium surrounds the pycnidium and covers it over. If 
these are embedded and sectioned, they will be found to contain a 
loose tangle of undifferentiated hyphe surrounding a central pyc- 
nidium. But as soon as the cork layer is broken the stroma under- 
goes a change. There is a rapid increase in size and at the same time 
a differentiation of the cells at the tips of those branches which 
reach the exposed surface. These cells now become shorter and 
thicker, acquire heavier walls, and are densely crowded together, so 
that in cross section they appear as a pseudoparenchymatous tissue. 
The layer thus formed covers all the exposed surface of the stroma 
and also grows up around the necks of the perithecia. The stroma 
increases very rapidly in size and a mass of stromatic tissue is 
formed beneath the pycnidia, which are thus pushed out through 
the cork layer into the periphery. The primordia of the perithecia 
are formed usually in the tissues of the bark below the base of the 
original pycnidium, but at times are formed well up in the stroma. 
Usually 15 to 30 perithecia mature in a stroma. 
According to the writers’ observations, the Tulasnes’ description 
(83, pp. 87-89) is substantially correct so far as it goes. They, of 
course, placed pycnidial material of Endothia gyrosa in the same 
species with FZ. fluens, but, as already noted, they observed the dif- 
ference in the structure of the stromata and aptly compared the 
pycnidial stroma of Z. gyrosa, as seen in section, to a Gautieria. 
The division of the stroma into ectostroma and entostroma made 
by Ruhland (67, p. 16) has, at least in the species of Endothia, 
no validity whatever. While it is true that pycnidia usually occur 
in the portion of the stroma first developed and perithecia often 
develop below them, this is by no means an invariable rule; and 
while stromata are developed which contain only pycnidia, other 
stromata apparently produce only perithecia or no spores whatever. 
Certainly no portion of the stroma can be distinguished which in- 
variably produces only perithecia or only pyenidia. On the con- 
trary, there is great variation in the relative position and time of 
appearance of the two types of fruiting structures. Also, while 
