802 



JOURNAL OF THE ROYAL HORTICtlLTURAL SOCIETY. 



functions to perform, which vary in their relative importance from one 

 species of plant to another. — R. B. 



Lig-ht: Determination of the Optimum Luminosity for 

 Plants in Different Stages of Development. By Eaoul Combes 

 [Ann. Sc. Nat. xi. Nos. 2, 3, 4, pp. 75-254; 42 figs., 5 plates).— This 



paper is illustrated with series of striking figures from photographs 

 of plants growing under different conditions of illumination, plants 

 accustomed to strong light, such as Triticum vulgar e, Mercurialis 

 annua, Pisum sativum, Salsola Kali, Solanum tuberosum, &c. With 

 plants accustomed to strong light, such as Amaranthus retro flexus , the 

 author finds a better development correlated with increased luminosity ; 

 but with plants accustomed to shade, such as Teucrium Scorodonia, 

 plants become more strongly developed as the luminosity decreases. 

 In the case of Solanwm tuberosum the most favourable result with 

 respect to the number of tubers and their weight was obtained from 

 plants grown in the strongest light used. 



The author establishes in his summary: — • 



1. Variation in the optimum luminosity during plant development. 



2. That the curves of variation of the optimum luminosity diffej" 

 for different physiological phenomena, such as, for instance, chloro- 

 phyll assimilation, germination, development of flowers and fruit, 

 maturation of fruit, &c. 



3. That each plant investigated, taking all the factors into con- 

 sideration, possesses characteristics of its own with respect to the 

 optimum intensity of light. — A. S. H. 



Lig-ht: On the Adaptation of Plants to Diffuse Daylight 

 and to Direct Sunlight. By J. Wiesner {Aim. Jard. Bot. Buit. 

 3rd supp. 1st part, 1910, pp. 47-60).— Wiesner finds that the 

 adaptations of plants are of such a character as to enable the leaves to 

 obtain the greatest possible amount of diffuse light, but to avoid as far 

 as possible the greater intensities of direct sunlight. In the case of the 

 False Acacia (Robinia Pseudacacia) the leaflets are spread out hori- 

 zontally to diffuse daylight, but when strong direct sunlight falls upon 

 them they move upwards upon the rachis, so that the leaflets upon one 

 side of the rachis form a more or less narrow angle with those on the 

 opposite side. In such a position the direct rays of sunlight no longer 

 fall upon the surface of the leaflets. 



In other plants which possess no power of movement the shape of 

 the leaves is different according as they are exposed to direct sunlight 

 or to diffuse light. Thus in the case of Syringa vulgaris Wiesner found 

 that the outer leaves of the plant which are exposed to the direct rays 

 of the sun are not flat, but that the leaf lamina is bent upon the mid- 

 rib, so that its two lateral halves are raised up and form an angle with 

 one another. Direct rays of sunshine are avoided by this modification. 

 The inner and lower leaves, which are screened by the outer leaves 

 from direct sunlight, are quite flat, and by this means obtain as much 

 diffuse light as possible. Other adaptations are mentioned in the 

 paper. — R. B. 



