go BOTANICAL GAZETTE {July 



of maximum geo-stimulation both because gravity acts at right angles to the 

 organ and because no longitudinal components are present. 



Dewers 5 has applied the Piccard rotation method to determining the 

 distribution of geo-sensitiveness in various plant organs. 6 In the root of 

 Lupinus albus the greater sensitiveness lies in the terminal 2 . 5 mm. The hypo- 

 cotyl of Helianthus always gives a permanent 5 response due to low irritability 

 and slow conduction of the stimuli. The method does not determine the dis- 

 tribution of geo-sensitiveness in this organ. In Hordeum vulgar e, Panicum 

 miliaceum, and Setaria italica, the coleoptile is much more sensitive than the 

 internode, although the internode is slightly sensitive in all these, most so in 

 Panicum. The sensitiveness in the coleoptile of Hordeum is about equally 

 distributed, so that when about half of the organ projects across the axis of the 

 centrifuge an 5 response occurs which later entirely straightens out. Appar- 

 ently there is about equal acropetal and basipetal conduction of the stimulus 

 in the two directions. Whether this occurs by separate paths in the two direc- 

 tions is not known. The geo-irritability of the internode of Panicum is higher 

 than that of Sorghum, while the reverse is true of photosensitiveness. In general, 

 however, Dewers finds that geo-conduction and photoconduction and reaction 

 run parallel in these organs. In general, those organs that show quick per- 

 ceiving power show rapid conduction, and those showing slow perceiving power 

 show slow conduction. The coleoptile of Hordeum belongs to the first class, 

 and the hypocotyl of Helianthus to the second. In an "Anhang" the author 

 reports that he was unable to find a destarching agent, for the purpose of 

 throwing some light on the statolith theory, the application of which did not 

 greatly injure the root. He tried A1 2 C1 6 and A1 2 (S0 4 ) 3 alone and in combina- 

 tion with Knop's solution and KH 2 P0 4 . 



Porodko 7 has studied chemotropic response of roots to various alkalies 

 and alkali earth salts. The experiments consisted of a square millimeter of 

 filter paper saturated in the salt solution applied to the side of the roots in 

 darkened moist chambers. In lower concentrations positive chemotropic re- 

 sponses occurred; in higher, negative chemotropic responses; and in still higher 

 positive, chemo-traumatic responses. Porodko asserts that the first response 

 is a true tropic response, for perception is localized in the tip, bending is due 

 to growth, and the concentration producing the response is comparatively low. 

 It is also not osmotropic, for the concentrations producing it in the various salts 

 show great variation. The positive and probably the negative response is due 

 to the action of ions. The effect of the ions beginning with those most effect- 



s Dewers, F., Untersuchungen iiber die Verteilung der geotropischen Sensibilitat 

 an Wurzeln und Keimsprossen. Beih. Bot. Centralbl. 3i r :309-357. 1914- 



6 For methods see Bot. Gaz. 47:482, 483. 1909; and Pfeffer's Plant physiol. 

 Eng. ed. 3:419- 



7 Porodko, Th. M., Vergleichende Untersuchungen liber die Tropismen. Ber. 

 Deutsch. Bot. Gesells. 32:25-35. 1914. 



