232 THE JOURNAL OF BOTANY 
the tropistic reaction varies. When the amount is small, the first 
effect is a + curvature followe by a — curvature; when the 
amount of CO, is larger, a — reaction only occurs. 
It is noteworthy that the rate of reaction is very quick ; after 
five minutes’ exposure to the diffusing stream of CO,, curvature 
can be recognized by the aid of the horizontal microscope. 
er experiments lead the author to lude that t 
of the results of stimulation occurs, @.e. that the perception- and 
ou 
Polowzow then passes on to the examination of geotropic 
tresponse, and shows that the reaction time is much shorter than 
time e 
review their own subject from a philosophical standpoint. This 
FREDERICK KEEBLE. 
Handbuch der Systematischen Botanik. Von Dr. Ricnarp R. v. 
WETTSTEIN, ii., Teil 2 (zweite Hiilfte). Royal 8vo. 
Pp. 395-578, with 104 illustrations, including 700 figures. 
Leipzig & Vienna: Deuticke. Price 8 marks. 
Tue present instalment forms the concluding section of Prof. 
Wettstein’s excellent Handbook ibuti 
marked Even as there are some ¢ oripetalous groups (or at 
least groups with choripetalous characters) amo Sympetale, 
placed among the Monochlamydex. The Sympetalous Families are 
arranged in ten series (or orders). Compared with Engler’s system 
