134 BOTANICAL GAZETTE : [avaust 
NOLES FOR STUDENTS. 
IN A SOMEWHAT extended paper on geotropism$ Dr. F. Noll controverts 
with much vigor Czapek’s theory of geotropism, as expounded recently’ 
Czapek holds that since gravity and centrifugal force act alike upon plans 
this can only be because both impart mass acceleration, and this can manifest 
itself only in pressure of tissue elements or even layers of tissue upon oe 
another. Thus there will be minute differences of radial pressure on differ- 
ent sides of the cortex which must be perceived and responded to by the 
growing cells. Orthotropic organs seek to equalize such pressures on the 
flanks ; plagiotropie organs (dorsiventral or radial) seek to realize a certal 
difference of pressure to which they are attuned. To support this view he 
appeals to the elimination of geotropic effects by the clinostat under propt 
conditions, and to the behavior of dorsiventral organs both flat and rolled o 
folded. To this theory Noll strenuously objects. He concludes that the 
sided stimulus of gravity into an all-sided intermittent one. In radial orgals 
rotation prevents curvature, but not in dorsiventral organs, which, even 0 
the clinostat, show geotropic (pseudo-epinastic) curvatures. eo 
Experiments on various organs, ingeniously subjected to artificial ie 
pressure equal to that of gravity, resulted negatively. Furthermore 
peduncles of Tropzolum, Linaria, etc., which with age reverse | 
anatomical structure, to show that the coarser cell structure has 
to do with geotropic sensitiveness, 
_ At the close of his paper Noll suggests a possible structure for pe : 
tive apparatus, which must be located in the ectoplasm in order t0 jbl 
necessary fixed orientation. The plasma has a tendency to form fC 
centrosphere-like bodies and the receptive apparatus may well be a 
S NOLL, F.: Ueber Geotropismus. Jahrb. f, wiss. Bot. 34: 457-506 me 
° CZAPEK, FRIEDRICH: Weitere Beitrige zur Kenntniss der geotropische? 
bewegungen. Jahrb. f, wiss, Bot. 32: 175-308. 1898. : 
7 Berichte d. deutsch. bot. Gesells. 15:516. 1897. 
