MOVEMENTS OF IRRITATION. 481 



under side of the leaves, which are well supplied with stomata, 

 and bring them into a moist space. After a shorter or longer 

 time we determine that the pollen tubes in their growth show an 

 inclination to direct themselves towards the stomata, and enter 

 them. If the leaf has only been, injected with water, the tubes 

 grow over the surface indifferently in all directions. Cane-sugar 

 is therefore a body which incites the pollen tubes to chemotropic 

 movements. 



The germinal hy plane of fungi are also chemotropically irritable. 

 If Tradescantia leaves are injected with 2 per cent, cane-sugar or 

 meat extract, and Mucor spores are then germinated in the moist 

 space on their under surfaces, we find here also that the tubes 

 turn towards the stomata, and enter them. If the concentration 

 of the cane-sugar solution is reduced toOl per cent., the tubes only 

 give a very feeble positive reaction ; the same is the case when the 

 concentration of the sugar solution is considerable (e.g. 20 per 

 cent.). 1 



1 See Molisch, Sitzungsber. d. Akad. d. Wiss.zu Wien, Bd. 102, Abth. 1, July, 

 1893; Miyoshi, Botan. Zeitung, 1895, and Flora, 1894. 



184. Movements of Foliage Leaves and Floral Structures Induced 

 by Changes in Illumination and Variations of Temperature 

 (Nyctitropic Movements) . 



There exist many foliage leaves and flower leaves which, as the 

 experimental researches of several physiologists have shown, react 

 by growth movements only to an insignificant extent in response 

 to variations of temperature, but conspicuously in response to 

 changes in illumination. We will first endeavour to make out 

 some of the phenomena in question. 



We make our observations on plants of Impatiens parviflora, 

 Chenopodium bonus Henricus, and Mirabilis jalapa, growing in 

 the open. The movements which interest us are clearly exhibited 

 in the younger, not yet fully developed foliage leaves. In the 

 daytime, these leaves are disposed more or less horizontally ; at 

 night they assume another position. In Chenopodium, and 

 especially in Mirabilis, the leaves raise themselves in the evening, 

 while in Impatiens they sink at this time, and hence as darkness 

 conies on they pass from a horizontal to a vertical position. On 

 the following day the leaves return again to their light position. 



P.P. I I 



