216 DIVISION II.—COURSE OF DEVELOPMENT OF FUNGI. 
no longer be recognised, so that the perithecium in the mature state is broadly 
ovoido-conical with an indistinct ostiole. The wall is formed of three or four layers 
of not much thickened elongated cells. 
Phyllachora Ulmi appears to show similarity to the process here described. 
11. The club-shaped stroma of Xylaria polymorpha (Fig. 103) consists in the 
young state, according to my earlier observations, of a white medulla surrounded 
by a firm black rind. The former is composed of an air-containing tissue of 
colourless hyphae; the rind of the portion bearing perithecia consists of small-celled 
pseudo-parenchymatous tissue, which is overlaid on the outside by the hymenium 
which bears gonidia (see section LX XI) and ultimately disappears. The primordia 

FIG. 103. Xylaria polymorpha, A, B, C transverse sections through young stromata with perithecia divided more or 
less exactly in half, all three magn. go times. > rind, 2 medullary layer of the stroma. 4, 5 very young perithecium cut 
through the middle, 7 a similar one cut through near the median plane, ¢ older perithecia, 2 gonidial layer. 2 perithecium 
with the mouth % bursting through the rind. C a nearly fully developed perithecium ; the section passes close to the mouth, 
which is fashioned as at g in A, elsewhere through the median plane; / the outer, z the inner wall of the perithecium, 
x the large-celled paraphyses filling the centre of the perithecium having entirely displaced the short-lived inner tissue, 
A the inner surface of the wall with the insertions of the paraphyses and asci. 
of the perithecia (4, #) make their appearance in the form of small spherical bodies 
which lie in the medulla close beneath the black rind, and are at once distinguished 
from the medullary tissue by containing no air and therefore being transparent. 
They are formed of a closely woven mass of slender hyphae, which are much 
thinner than the hyphae of the original tissue and must therefore be a new formation 
in it. In somewhat older specimens an irregular large-celled coil of tissue is found 
lying in the middle of the sphere. The spheres now increase in size in the direction 
of the medulla, the shape, structure, and position remaining the same. Then a 
dense tuft of straight hyphae, in the shape of a broad truncated cone, shoots forth from 
the part which abuts on the rind, and elongates in the direction of the rind, which is 
