PLANT-PHYSIOLOGY 931 
comparing specimens of one plant with a long series from Central 
Europe, Mr. Williams concludes that they should be referred to 
G. campestris epee than to G. Amarella, notwithstanding some 
difference in habi 
—- Wis PH 
Untersuchungen iiber Pease eres paeMaee bet den ONE Mit 
Beriicksichtigung der Einwirkung von Gases und der geo- 
tropischen Heizoracheinungen Von ins. PoLowzow. 
Pp. 229. Mit 11 Abbildungen u. 12 Kurven in Text. Jena: 
Gustav Fischer. 1909. 6 marks. 
NoTWITHSTANDING the fact that during recent years many 
investigations into the phenomena of irritability have been under- 
_— our ae of this branch of plant-physiology remains 
vague. This is the case not only with respect to the mechanism 
of Bates asnse, but also with respect to the simpler factors of 
irritability which admit of precise measurement. For example, 
m 
according to Czapek, in the hypocotyl of Helianthus annuus, 
twenty minutes; according to Fitting, five to six minutes; and, 
according to Bath, three minutes. urther investigations as to 
t ual cou f events in the reaction of plants to stimuli, 
of gases—a type of irritability selected for these investigations 
because it gee received but little attention—and of the response 
to gravity, selected for the converse reason. 
he question of directive response of plants to gases has been 
not only are roots capable of responding eroidotropistically to 
certain gases, but that shoots exhibit a similar reaction 
ants experimented with consisted for the most part of 
re of Helianthus annuus grown in pots. The plants were 
jar through glass-tubes. A porous tube, connected with the gas 
supply-tubes and standing in a definite position with respect to 
the plant, allowed of the diffusion of the gas, which thus reached 
bell-jar was prevented by absorption or by sweeping out the gas 
under the bell-jar by a siphon arrangement. The results of the 
experiments show that both aia dioxide and oxygen set up 
tropisms, whereas hydrogen and nitrogen are inert. The positive 
results obtained by earlier investigators with nitrogen are shown 
to have been due to the presence of traces of ammon 
According as the diffusing CO, is small or large i S ‘amount, so 
