30 NORTH AMERICAN SORDARIACEAE 
To guard against errors produced by heliotropic curvatures, 
the plants were grown in some cases in complete darkness; in 
others they were placed a short distance below the window sill so 
that the perithecia would grow without curvature as much as possi- 
ble. From such cultures the higher distances of spore ejection were 
obtained. It is interesting to note in this connection that Woronin, 
working with this same species, found a much greater distance, 
sometimes as high as 15 cm. This is really remarkable when we 
stop to consider that the perithecia do not usually measure over .7 
mm. and the asci only about a third of this length. 
Attention was called on a previous page to the spores remain- 
ing in the apex of the expanding ascus. This appears to be due 
to two factors, one of which is purely physical and the other 
physiological and structural. It was noted that the apex of the 
ascus does not stretch ; inasmuch as the lateral walls do, they be- 
come separated from the spore mass and from whatever protoplasmic 
and gelatinous content the ascus may have, at all points except the 
apex. The attachment is very slight, but there is some adhesion 
between the appendages and the wall at this point, and it remains 
undisturbed until the ascus ruptures. The arrangement of the 
spores is usually unaffected also, as they are held in place mainly 
by the gelatinous appendages. The other force which assists to 
keep the spores in the apex of the ascus is the buoyancy of the ab- 
sorbed water which causes the turgidity of the ascus. That the 
two forces operate is evident from the fact that the spores are 
heavier than water and that they follow the apex of the expanding 
ascus when it lies on its side in water. 
In the genus Sordaria there occurs a different and somewhat 
less efficient mechanism for spore dissemination, at least this ap- 
pears to be the case judging from the frequent appearance of 
clogging of the canal leading through the beak. (PX. 78. f. 14.) 
The ascus stretches here as in the genus Pleurage, but there is 
less tendency to lateral extension, the asci stretching mainly in 
length. When a mature perithecium of S. fimicola, for instance, is 
ruptured under a cover-glass, the asci often appear with long wide 
pedicels, but they will be but slightly wider than the normal ascus. 
In every species of this genus reported for this country at least, 
there occurs a very characteristic ascus apex. ) 2. f. 2, 17.) 
