RECENT ADVANCES IN SCIENCE 395 



The evidence is derived from a microscopic examination of the 

 distribution of these starch grains in a number of species. A 

 somewhat detailed examination was made of the reproductive 

 organs of liverworts in which a good development of statolith 

 starch grains was found to correspond with power of response to 

 the gravitational stimulus. Reference has already been made to 

 Demole's work on the negative geotropism of bracken fronds. 

 Miss Prankerd finds that in ferns a statolith apparatus develops 

 at the physical apex of the fronds. On the contrary in organs 

 where curvature is impossible or of no advantage to the plant, 

 statoliths could not be detected. In some cases chloroplasts 

 function as statoliths, as for example in Ophioglossum, Lunaria, 

 and Myriophyllum. 



That geotropic stimulation affects the viscosity of the 

 protoplasm is a view put forward by G. and F. Weber (Jahrb. f. 

 wiss. Bot. 57, 129-88, 1 91 6), who based their conclusion on 

 observations on the rate of fall of starch grains in stimulated 

 cells of the endodermis of the epicotyl of bean seedlings (Phaseo- 

 lus multiflorus) as observed in longitudinal (radial and tan- 

 gential) sections. This conclusion is destructively criticised 

 by Clara Zollikofer (Ber. deut. bot. Ges. 35, 291-8, 191 7), who 

 holds that G. and F. Weber neglected the large experimental 

 error in their crude method, so that the results obtained by 

 them are meaningless. 



Small {Ann. of Bot. 31, 313-14, 191 7) upholds the conclusion 

 that the Weber-Fechner law holds for perception of geotropic 

 stimulus by plants, a suggestion put forward by Darwin and 

 supported by Fitting. It is further proposed by Small that 

 the perception of geotropic stimulation is correlated with 

 permeability, since changes in the electrical conductance of 

 the stimulated tissue, which are assumed to be a measure of 

 the alterations in permeability, also increase with the in- 

 tensity of the stimulus according to the Weber-Fechner law. 

 But when we consider that it has yet to be proved that elec- 

 trical conductivity is a measure of permeability, and that 

 indeed permeability is a term used in a variety of different 

 senses, and that Small has not defined what he means by it, 

 although he uses it in a quantitative sense, it becomes clear 

 that Small's hypothesis that geotropic stimulation is connected 

 with permeability changes rests on no very firm foundation. 

 A remark of Verworn's is apposite in this connection: " Un- 



