Discharge of Spores of Leptosphseria acuta. 141 
and since no account of the phenomenon in the present species 
seems to have been given by anyone previously. 
Leptosphceria acuta, a Pyrenomycete of the family Pleosporacese, 
occurs on herbaceous stems, and is very common over almost the 
whole of Europe. It is very readily to be found during winter and 
spring upon the bases of decaying nettle (Urtica dioica) stems. The 
black shining perithecia (Fig. 1) are separate, no stroma being 
present, and are at first immersed in the cortex of the stem, but by 
the decay and falling off of this cortex they come to he freely 
exposed, each being firmly fixed by its broad base to the wood of 
the stem. The perithecia are hemispherical or more or less conical, 
about J mm. high, with a prominent wart-like ostiole; the wall of 
the perithecium is tough and coriaceous, and composed of dark- 
coloured plectenchyma. The asci (Fig. 2) are cylindrical when 
mature, 150// to 200// long, containing 8 fusiform biseriate yellowish- 
brown spores, each of the latter being 50// to 58// long and 
transversely septate. The number of septa varies, but usually 
there are from 10 to 13, while each cell contains one or several 
oil-guttules. The spores are often slightly curved. The hyaline 
wall of the mature ascus consists of two layers, an outer thin 
inextensible cuticular layer which does not swell when immersed in 
water, and an inner gelatinous coat which absorbs water very 
readily, and is thereby capable of swelling to a considerable extent. 
Among the asci are numerous filiform septate paraphyses whose 
walls are likewise somewhat gelatinous, and swell up in water. 
When a ripe perithecium (the perithecia ripen during winter 
and early spring) is cut open and the hymenium carefully withdrawn 
with a needle and mounted in a drop of water on a slide, the 
rupture of the outer coat of the ascus wall by the inner coat at the 
apex of the ascus can frequently be observed, providing the asci 
are fully mature and have not been detached from the sub- 
hymenial layer, or injured in any way. This rupture (Fig. 3) of 
the outer cuticular coat at the apex is brought about by the 
increased turgidity of the ascus, induced by endosmosis, and 
probably also to some extent by the absorption of water and con¬ 
sequent swelling of the inner gelatinous layer. The latter breaks 
through almost explosively, and elongates suddenly through the 
apical cleft to about the distance shown in Fig. 3; that is, to about 
1^ times its original length, at the same time broadening out 
somewhat in its upper extruded part. The inner gelatinous tube 
with its spores, which always tend to remain in the upper part, 
continues to elongate, often at a fairly rapid rate, reaching in a few 
