386 SUMMAKY OF CURRENT RESEARCHES RELATING TO 



hand, Pick has shown that the shape and arrangement of assimilating 

 tissues are certainly controlled to some extent by the presence of full 

 sunlight or of shade. Both of the foregoing works were preceded by 

 a paper by E. Stahl in which the influence of the intensity of light on 

 the structure and arrangement of chlorophyll-parenchyma was pointed 

 out. It may be further stated that the same author had previously 

 studied the effect of the direction and intensity of light on some 

 movements in plants. In a jJaper just imblished E. Stahl incorporates 

 some of the earlier results obtained by him, and adds several facts of 

 considerable interest. The thesis may be stated as follows : The 

 elongated or palisade cells are best adapted for light of high inten- 

 sity ; the looser parenchyma for that of low intensity. (To this in 

 passing may be added Areschoug's observation that the looser or 

 spongy parenchyma is that best adapted for transpiration, and 

 characterizes the foliage of moist climates ; where either local or 

 climatic relations render too rapid transpiration undesirable, these 

 layers are protected by a palisade system.) The author has devoted 

 most attention to plants which can endure shade as well as bright 

 sunlight, and here wide differences are alleged to exist between the 

 forms growing in light and those found in shade. All the differences 

 are of the character above described, namely adaptation to sunlight by 

 the development of a better palisade system. The critical point of 

 the investigation is plainly that leaves develojung in sunlight have a 

 less strongly characterized spongy parenchyma, and a better marked 

 palisade system. In view of the fact that these two systems are 

 generally found as stated in the thesis, the author asks whether this 

 ought not to influence our treatment with plants in greenhouses. 



Position of Leaves in respect to Light.* — E. Mer states that 

 certain parts of the leaf, usually the limb, receive luminous impres- 

 sions, while other parts, as the petiole, the motile organs, &c., execute 

 movements for the purpose of placing the former in a favourable 

 position for receiving light. The mechanism of these movements 

 consists in an augmentation of growth, or only of turgidity, resulting 

 in curvatures and torsions. The presence of light seems indispensable 

 to these movements. 



Photepinasty of Leaves, f — W. Detmer proposes the term "phote- 

 pinasty " for the epinastic position of leaves induced by light. The 

 normal unfolding of leaves is due to paratonic nutation. Light first 

 induces stronger growth in the upper side of the leaf; and it is to 

 this phenomenon that he proposes to apply the term. 



Movements of Leaves and Fruits.J— The movements of leaf- and 

 flower-stalks in virtue of which they assume an inclined or horizontal 

 position are attributed by H. Vochting to various causes, geotropism, 

 heliotropism, and the weight of the flowers or fruit. In addition to 



* Comptes Rendus, xcvi. (1883) pp. 115G-9. See also this Journal, ante, pp. 

 235 237. 



t Bot. Ztg., xl. (1882) pp. 787-94. 



X Vochting, H., ' Die Bewegungen der Bliiten u. Friichte,' 199 pp. (2 pis.) 

 Bonn, 1882. See Bot. Ztg., xli. (1883) p. 13. 



