Physiology of the Spermatozoa of Ferns. 579 
matozoa do not move more than about ten minutes, and even 
at a concentration of o-ooi per cent, the swarm-period is 
reduced to about two-thirds the normal. 
The swarm-period is also much reduced when the sperma¬ 
tozoa are liberated in solutions of neutral substances which 
are concentrated enough to withdraw a considerable quantity 
of water from the organisms. Thus at a concentration 
isotonic with 2 per cent, potassium nitrate there is no forward 
movement, no swarming, for either cane-sugar, potassium 
nitrate or sodium chloride. At concentrations isotonic with 
1 per cent, potassium nitrate swarming takes place, but its 
period is much reduced. If, however, the hanging drops are 
isotonic with o*i per cent, potassium nitrate, the swarming is 
as active as in tap-water alone. The swarm-periods in these 
weak solutions were not exactly observed, but after forty 
minutes the spermatozoa were seen to move as actively as in 
similar experiments with tap-water. 
IV. The Starch in the Vesicle. 
It is well known that the spermatozoa of the Ferns carry 
with them a vesicle attached to the hinder end of their 
bodies. In this vesicle is usually a considerable quantity 
of starch in the form of small grains. 
The starch can readily be distinguished in the living 
spermatozoa whenever they move slowly enough for the 
purpose. It appears to occur under normal conditions in 
all freshly liberated spermatozoa. If a prothallium be plunged 
in a solution of iodine, the antheridia become more darkly 
stained than any of the vegetative cells. This is due to the 
relatively large amount of starch stored up in the mother- 
cells of the spermatozoa. The starch grains, often about 
ten in number, are chiefly collected on the side of attachment 
of the vesicle. 
According to Strasburger 1 the spermatozoa, on being 
attracted toward the archegonia, lose their vesicles in the 
1 Strasburger, Die Befruchtung bei den Farnkrautern, loc. cit., p. 403. 
