1 8 
F. Cavers. 
thrown upon this observation by Leitgeb (8), who investigated the 
development of the antheridia, and by Waldner (49), who worked 
out the embryology of the sporogonium ; in fact, neither of these 
writers could observe such threads at all. Schimper and other 
observers also noticed that the capsule sometimes contains very 
small spores which to a greater or less extent replace the ordinary 
spores. Schimper described these “'microspores ” as arising from 
the ordinary spores by repeated division, and Warnstorf suggested 
that Sphagnum is a heterosporous Bryophyte, the microspores 
producing male plants and the large spores female plants! How¬ 
ever, Nawaschin (20, 21) showed that the filaments and the 
“microspores” belong to a parasitic Fungus —Tilletia Sphagni — 
the life history of which he worked out, tracing the entrance of the 
mycelium into the developing capsule and its ramification through 
the archesporium, where it produces its own spores, mingled with 
those of Sphagnum or even, in small and deformed capsules, 
replacing them altogether. 
The dehiscence of the capsule is brought about by a curious 
and probably unique mechanism. It was long ago noticed that the 
capsule of Sphagnum explodes with a cracking or “ popping ” noise, 
the shape of the capsule suddenly changing from spherical to 
cylindrical, and the lid, together with the spores, being thrown out 
to a distance of several inches. The beautiful mechanism involved 
was explained by Nawaschin (22). As the ripe capsule dries, the 
delicate central tissue (columella) shrivels and is replaced by air, so 
that the capsule eventually contains, within the brown epidermal 
layer, practically nothing except the spore-sac (by this time an 
inverted saucer-like bag within which the spores lie loosely) and 
below this a relatively large air cavity. As drying proceeds, the 
longitudinal diameter of the capsule remains unchanged, but the 
transverse diameter is greatly shortened owing to transverse con¬ 
traction of the epidermis, and the imprisoned air is therefore 
compressed. During this change, the lid (firmer in texture than 
the rest of the wall) shrinks but little, a difference in tension is 
thus set up, and finally the lid becomes loosened along the annular 
groove and is forcibly shot off, along with the spores, in exactly 
the same way as a bullet from an air-gun. Nawaschin’s paper (22), 
should be consulted for details of his ingenious experiments and his 
determination of the volume and pressure of the air in this 
remarkable “ pop-gun ” capsule. 
The protonema of Sphagnum differs from that of most other 
