Sense Organs for Gravity and Light. 73 
shock not only prevents geotropism but also interferes with the 
regeneration of the statocytes. 
Another experiment 1 of Nemec’s is the following:— 
A transverse incision is made half way through a bean root 
close to the tip. The result is that a new root tip is formed at the 
basal lip of the wound, i.e. the one furthest removed from the root- 
tip, which acquires movable starch and finally replaces the old tip, 
which has meanwhile lost its statoliths. Twelve hours after the 
operation all the roots are geotropic because the old root-tip is still 
capable of functioning, not having lost its starch : seventy-two 
hours after the operation all the roots are also geotropic, but 
apparently for a different reason, viz., because, though the old root- 
tip has lost its movable starch, the new root-tip has developed 
statoliths. Between these stages (twelve and seventy-two hours 
after the operation) there is a critical period, about sixty-six hours 
after operating, during which some but not all the roots are 
geotropic. This corresponds to the facts that the old root-tip has 
lost its starch, while the new tip has not had time to complete the 
formation of new starch-statoliths. 
Czapek has made an ingenious point against the statolith 
theory. He showed that the roots of Lupine seedlings from whose 
roots half a millimetre has been removed still show the homogentisinic 
reaction when placed in the horizontal position. Now this reactiou 
is according to Czapek 1 a proof that the roots are geoperceptive, 
and he adds that since the amputation has removed the falling 
starch-grains, the act of perception cannot have taken place by 
means of statoliths. 
On the other hand it is denied by Nemec that the removal of a 
half mm. takes away the whole of the starch, and he brings other 
facts to bear against Czapek—a discussion into which we cannot 
now enter. 
Fitting objects to the statolith theory on the strength of his 
klinostat experiments, in which it will be remembered, he shows 
that, with an instrument rotating once a second, gravitation is 
continuously perceived by the plant. This is no doubt a difficulty 
but not, as it seems to me, an insuperable one. 
On the whole it is not unfair to claim that the evidence for the 
theory has gained rather than lost strength since 1904. 
Heliotropism. 
What is here given is taken from Haberlandt’s book 2 in which 
Ber. d. Bot. Ges. xxiii., 1905, p. 113. 
