1910] HOYT—FERTILIZATION IN FERNS 365 
forward. If these movements free them from the hindrance, they 
resume their normal movements; but if the hindrance continues, they 
perform other complex movements, finally performing almost every 
conceivable variety of movement that is possible for them, and they 
continue these movements until they die or free themselves from the 
obstacle. 
A few of the sperms showing the positive and negative reactions 
appear to turn directly toward or away from the stimulant. These 
Swing their anterior ends through large circles, rotating on their 
axes, and then go forward in the new direction. Such movements 
' often do not result, however, in the complete orientation of the sperms 
with respect to the stimulus; the final orientation is then attained 
by further successive swingings of their axes as they go forward. 
Most sperms attain their orientation by such small swingings of their 
axes toward or away from the stimulant as they go forward. 
Occasionally sperms collect in a definite region by passing into 
this without reacting, and then turning back whenever they tend to 
leave it. 
Finally, it has been shown that different sperms react differently 
to the same stimulus at the same time, and that the same sperm may 
react differently to the same stimulus at different times. In some 
cases these differences in reaction are due to different ee 
conditions induced by different past experiences. 
All these facts indicate that the reactions of fern sperms are due to 
the action of stimulants on the organism as a whole, and not to the 
direct action of a stimulant on local parts of the organism. The 
Sperms possess a certain mechanism of reaction, and this mechanism 
is called into play by a change of conditions or by an interference 
with the normal movements. This mechanism is different in differ- 
‘€nt sperms, and may be altered by different external conditions. 
The strongest evidence for the direct orientation of the axes of 
the sperms by the stimulant is furnished by those cases in which the 
‘perms respond by large swingings of their anterior ends and then go 
forward, turning fairly directly toward or away from the source of 
stimulation. Such cases do not prove, however, the “local action” 
theory of the reaction. These sperms may be regarded as having 
a mechanism of ‘response by which they swing about until they are 
