1910] HOYVT—FERTILIZATION IN FERNS 357 
PFEFFER (38, p. 757) suggests that, in rapidly reacting swarmcells, 
the positive, apparently “topotactic,” response may be the result of a 
series of negative responses as is outlined above, but considers the 
reactions of many flagellates, the swarmspores of many algae, the 
sperms of ferns, and the swarmspores of Saprolegnia to be accom- 
plished by tropistic orientation, “durch die typische tropistische 
Richtung der Kérperachse”’ (38, p. 754).?. The same view is held 
by Liprorss for the movements of the sperms of Marchantia and 
Equisetum. SHrBata explained the positive reactions of Isoetes 
sperms in the same manner, but considered certain negative reactions 
shown by them to be phobotactic, believing that both kinds of reaction 
exist inthesame organism. The same possibility is suggested by Lp- 
- Forss for the sperms of Marchantia. VoEGLER and BULLER do not 
discuss the nature of the reaction. _RoTHERT showed that certain 
bacteria react only in tending to pass from the optimum in the man- 
ner outlined above; they thus finally collect in the region of optimum 
stimulation. 
JENNINGS (18) has shown that the reactions of many of the lower 
organisms Consist of a series of random movements performed when 
the organism tends to pass from the optimum, with the continuance 
of such of these movements as take it toward the optimum. The 
movements leading toward the optimum may in Stentor and other 
organisms be performed more readily after repetition, and in some 
organisms the final response—toward the region of optimal stimula- 
tion—may be attained with practically no random movements, 
thus giving a directive reaction. The difference between this type 
of reaction and that favored by the holders of the other view men- 
tioned is, that in this one it is held that the stimulant acts on the 
organism as a whole and that the organism responds as a whole, 
performing complex and coordinated movements; in the other it is 
held that the stimulant acts on certain parts of the organism, directly 
modifying the action of these parts. According to JENNINGs, the 
reaction obtained depends on the physiological condition of the organ- 
ism, which is in turn partly determined by the past experiences of 
the organism. 
? The reference to the German ae is given here because of the abridgment of 
the English translation at this poin 
