ZOOLOaY AND BOTANY, MICEOSCOPY, ETC. 995 



ordinary air and in an atmospliere devoid of carbon dioxide, Herr 0. 

 Menze draws the following couclusious : — The dry weight of leaves 

 increases by day when assimilation is unchecked ; and this increase in 

 dry weight is due to the increase in the amount of assimilated starch. In 

 cut leaves the amount of sugar increases in the light, in consequence of 

 the absorption of starch. When leaves are exposed in light to an 

 atmosphere containing no carbon dioxide, they decrease in dry weight 

 from loss of starch, which is indicated by an increase in the amount of 

 soluble carbohydrates. 



Action of Light on Roots grown in "Water.* — M. Devaux gives the 

 results of some experiments he has made on the action of light on roots 

 grown in water. When exposed to light the growth of roots in water is 

 far less than when left in darkness ; hairs, however, are more abundant. 

 The ramification of roots exposed to light is feeble,' while if left in dark- 

 ness branches are quickly and abundantly formed. The pigmentation, 

 however, of roots exposed to light is strong, while in darkness it is 

 weak. 



Influence of Eadiant Heat on the Development of the Flower.t— 

 Herr H. Vochting has shown, by placing between the source of light 

 and an opening bud of Magnolia conspicua a solution of iodine in carbon 

 bisulphide, which has the power of completely absorbing the illumina- 

 ting rays of the spectrum, while allowing the dark heat-rays to j)ass, 

 that the curvature attendant on growth takes place just as in normal 

 sunlight. It must therefore be the non-illuminating rays to which 

 the growth is due. 



(3) Irritability. 



Electromotive Properties of the Leaf of Dionaea.l — Prof. J. Burden 

 Sanderson has continued his investigations into the electromotive pro- 

 perties of the leaf of Dionsea in the excited and unexcited states. They 

 confirm his previous conclusion, that the property by virtue of which 

 the excitable structures of the leaf respond to stimulation is of the same 

 nature as that possessed by the similarly endowed structures of animals. 

 He finds the two sets of phenomena termed those of the resting-current 

 and those of the action-current of the leaf — i. e. the electrical projjerties 

 possessed by the leaf when stimulated and those which it disjjlays when 

 at rest — so linked together that every change in the state of leaf when at 

 rest conditionates a corref;ponding change in the way in which it reacts 

 to stimulation ; the correspondence consisting in this, that the direction 

 of the response is opposed to that of the previous difference of potential 

 between the opposite surfaces, so that as the latter changes from 

 ascending to descending, the former changes from descending to 

 ascending. 



The author considers that this can only be understood to mean that 

 the constantly operative electromotive forces which find their expression 

 in the persistent difference of potential between the opposite surfaces, 

 and those more transitory ones which are called into momentary exist- 

 ence by touching the sensitive filaments or by other modes of stimula- 

 tion, have the same seat, and that the opposition between them is in 



* Bull. Soc. Bot. France, xxxv. (1888) pp. 305-8. 



t Ber. Deutsch. Bot. GeselL, vi. (1888) pp. 167-78 (1 pi.). 



X Proc. Koy. Soc, xliv. (1888) pp. 202-4. Cf. this Journal, 1882, p. 533. 



