Physiology of the Spermatozoa of Ferns. 575 
withdrawal of water, as the salts and sugar. The movement 
in alcohol and glycerine at high concentrations is not sur¬ 
prising if we draw what seems to be the justifiable conclusion 
that the rate of motion of spermatozoa varies (within certain 
limits) as the amount of water they contain. 
Glycerine penetrates living membranes much more slowly 
than alcohol. In my experiments it was found that at 
the concentration 1 mol of glycerine the spermatozoa did 
not immediately begin to move forward after liberation. 
After lying motionless for a short time they began to move 
slowly forward, at length reaching a maximum speed. In an 
isotonic solution of alcohol the spermatozoa moved quite 
rapidly as soon as liberated. The difference in the rate of 
penetration of the two substances into living membranes 
makes itself here clearly apparent. Glycerine requires a 
considerable time to penetrate. Hence the recovery of the 
spermatozoa. Alcohol penetrates almost instantaneously. 
Hence the rapid movement of the spermatozoa at the con¬ 
centration 1 mol of this substance immediately after their 
liberation. 
It was noticed that the spermatozoa did not move so 
rapidly in F mol potassium nitrate as in T V mol cane-sugar. 
This result, which was repeated several times, may possibly 
be accounted for by the more toxic action of the salt. It 
may, however, indicate that the membranes of the organisms 
are to a slight degree penetrable by cane-sugar. 
III. Length of the Swarm-period. 
According to Strasburger 1 the swarm-period for the sper¬ 
matozoa of Pteris serratula is not more than half an hour, 
while for Ceratopteris thalictroides it is scarcely twenty 
minutes. Voegler 2 has confirmed the latter observation and 
has also made the following additional swarm-period deter¬ 
minations :—Gymnogramme Laucheana , twenty-five minutes ; 
1 Strasburger, Die Befruchtung bei den Farnkrautern. Jahrb. f. wiss. Bot., 1869- 
70, Bd. vii, p. 396. 2 Voegler, loc. cit., Bot. Zeit., 1891, pp. 646-648. 
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