1922] LUPO—HYPOXYLON 491 
Other peculiarities of this part are the brown mottled appear- 
ance of the whole region, due probably to irregular depositing of 
some substance in the walls, and the further zonation of this por- 
tion of the stroma (fig. 1). This last character is one of the peculiar 
taxonomic features of Daldinia, and in Hypoxylon is not evident 
except through the microscope. These parallel markings are due 
- to irregularities in growth that result in a region of short cells 
bordering a region of long cells, and to the hyphae intertwining 
more at this point. 
On the outer edge of this portion of the stroma the large hyphae 
end at varying levels, sometimes with a club-shaped enlargement, 
and do not give a definite line of demarcation. From between 
these the two types of hyphae rich in protoplasm pass out to form 
the upper layers, and of these the larger do not pass much beyond 
the lower part of the perithecial zone, where some of them form the 
fruiting bodies, and the smaller continue on beyond this to form the 
three superficial boundaries. It is this situation which indicates 
that the sizes of these hyphae were differentiations according to 
function and not accidental variations. In this region of scattered 
hyphae that form the perithecial layer, and also in the three outer 
regions, the cells are typically binucleate, although a very few with 
several nuclei are seen; and this is true also for the hyphae forming 
the perithecial wall. On the outer surface of the stroma are spheri- 
cal excrescences like bubbles, and these are related to the inter- 
hyphal spaces. They are probably the excretion of some oily 
substance through the stroma, and it is owing to this that the young 
stromata feel smooth and slightly greasy to touch. 
Formation of perithecia and ascogonia 
In the formation of perithecia in Hypoxylon the first evidence 
of their origin is the coiling of hyphal ends or of branches. As 
already stated, it is the larger of the two protoplasm-filled hyphae 
differentiated from the substratum that do this, and apparently 
they do not show any increase in size before or immediately after 
this stage. Other hyphae of the same size surround these initial 
coils and form a small circular knot (figs. 7-9), which was the earliest 
stage Brown recognized in the development of the perithecia in 
