146 Discharge of Spores of Leptosphseria acuta. 
ively through an apical pore. Sphceria Scirpi, however, apparently 
differs from Leptosphceria acuta in being able forcibly to discharge 
its spores while the perithecia are under water. De Bary also 
mentions Sphceria {Leptosphceria) Lemanece, Phyllachora Ubni, 
Cordyceps and Claviceps, as examples in which the spores are 
successively discharged in a forcible manner. Doubtless many 
other Pyrenomycetes discharge their spores in this way—especi¬ 
ally among the Pleosporaceae where the ascus wall has the 
characteristic double structure described above in Leptosphceria. 1 
However, it does not follow that all those forms with a double 
ascus wall discharge their spores explosively, although in all the 
Pleosporaceae the inner gelatinous layer breaks through the apex 
of the outer membrane and elongates considerably, the spores 
following this elongation pari passu in the upper part of the tube. 
This suffices to carry the spores out through the ostiole, where, 
providing they are not forcibly ejected, they may be washed away 
by rain or dew, the process being the same as that occurring in 
Leptosphceria acuta when the perithecia are in water. In the 
common Pleospora herbarum de Bary 2 mentions that the spores 
usually remain in the elongated ascus tube, although sometimes 
they may be shot out forcibly. Thus both methods of spore- 
dispersal may occur in one and the same species, as is the case 
with Pleospora herbarum and Leptosphceria acuta, as well as probably 
many others. 
The spores of Leptosphceria acuta readily germinate in moist air 
a few hours after their discharge, the two end cells of each spore 
usually putting out germ-tubes first (Fig. 15), followed later by 
others from one or two of the central cells. No case was observed 
where every cell of a spore had sent out germ tubes. 
Some simple experiments were conducted in order to deter¬ 
mine whether light has any directive influence upon the discharge 
of the spores, but no such influence could be detected. The spores 
were found to be ejected in the same direction when the perithecia 
were subjected to strong unilateral illumination, as they were when 
in darkness, or illuminated equally all round. Heliotropic sensi¬ 
bility, such as is shown by the asci of Ascobolus, would not be of 
much use in the case of the present species, the perithecia of which 
are clustered on vertically placed dead nettle stems, and point 
their ostioles horizontally to all points of the compass, thus being 
very unequally illuminated. The spores are presumably ejected on 
to and infect the young nettle shoots which come up in spring, the 
time when the asci are mature. 
1 See Engler and Prantl, “ Nat. Pfl.,’ Teil I., Abt. I. 1897, p. 428. 
* Loc cit., Legend of Fig. 47, p. 95. 
