546 SUMMARY OF CURRENT RESEARCHES RELATING TO 



statolithic views of Haberlandt and Nemec. Their theory may fairly 

 hold the field until better theories of both gravi-perception and of the 

 function of falling starch-grains are established. 



Aerotropism in Roots.* — Mary E. Bennett has carried out a series 

 of experiments on the supposed aerotropic curvatures ascribed by 

 Molisch to roots. Roots of maize, Pisum sativum, Raphanus sativus, 

 and others were subjected to the one-sided access of oxygen, hydrogen 

 and carbon dioxide, to determine whether the roots do really curve 

 toward or away from these gases in natural or artificial conditions. 

 When the roots were grown in water between submerged chambers, the 

 one containing air and the other C0 2 or hydrogen, no constant and 

 regular curvatures occurred ; the majority of roots were indifferent to 

 the influence of any of these gases. The same results followed when 

 the roots were not submerged but placed between the gas chambers in a 

 larger damp chamber. When the seedlings were grown in a thin 

 vertical layer of earth forming a septum between air and C0 2 , or air 

 and hydrogen, or in earth permeated on one side with air, and on the 

 other with C0 2 or hydrogen, very few curves were formed, the large 

 majority of roots growing straight, or if curved, the curves were not 

 directed by the presence of gases. Similarly, when the roots of seedlings 

 were grown in a thin layer of gelatin between different gases, no curves 

 of constant direction were shown. In experiments similar to those of 

 Molisch, where roots were supported close to narrow slits opening into 

 gas-chambers from which gases were constantly diffusing, curves were 

 produced generally towards the gas-chambers, whether or no gases were 

 diffusing from the chambers. But these curves were found to be purely 

 hydrotropic. The author concludes that, at any rate in the case of the 

 land plants used in the present inquiry, definite direction curvatures are 

 not induced in roots by the one-sided access of gases, and these roots 

 are therefore not aerotropic. 



Stimulating Action of some Metallic Salts on the Growth of 

 the Higher Plants. f — Masayasu Kanda finds that a favourable influence 

 is exerted on the growth of some plants by a slight addition of certain 

 metallic salts, which are not nutrient but act as poisons in larger doses. 

 The methods which gave satisfactory results were those of water-culture 

 and pot-culture, both of which in the case of land plants imply a de- 

 parture from normal conditions. The author found that very dilute 

 copper sulphate solution (0* 000000249 p.c.) acted prejudicially on 

 pea-seedlings in water-culture, while still further dilute solutions 

 (0-0000000249 to 0*00000000249 p.c.) acted neither as poison nor 

 as stimulus. In certain " soils, however, the same salt had a favourable 

 action on pea- and bean-seedlings. Very dilute solutions of sulphate 

 of zinc had a favourable action ; the optimum concentration lies 

 between 0' 00000287 and 0*0000001435 p.c; a concentration of 

 0*0000287 p.c. had a poisonous effect. Pot-plants of Vicia and Pisum 

 watered three times a week with 200 c.cm. of 0*287 p.c. solution of 

 zinc-sulphate, showed a more rapid growth than the control plants 



* Bot. Gazette, xxxvii. (1904) pp. 241-59 (5 figs, in text). 



t Journ. Coll. Sci. Imp. Univ. Tokio, xix. Art. B (1904) pp. 1-37 (1 pi.). 



