659 



about 30 per cent., and a straw yield about 32 per cent, less than the un- 

 shaded plants in the same fields. 



The results which PagnouP obtained are especially noteworthy. In 

 experiments with sugar beets, he found a strong falling off in sugar content 

 with an increase of the leaf substance per gram of root body and, for pota- 

 toes, a decreased tuber yield with a significant falling off of dry substance. 

 Besides this, however, he proved that the nitrate content for beets and 

 potatoes, grown under blackened glass, was more 'than ten times as great in 

 the leaves and roots as in plants grown in the sunshine. Therefore, the 

 physiological activity was changed in the shade since the nitrates were not 

 sufficiently used up. 



Some of v. Oven's experiments took up the measurement of the inten- 

 sity of the light which remained after the sun's rays had passed through a 

 tree crown. It was shown by the Bunsen-Roscoe method, that the propor- 

 tion of full daylight to the amount of light under fruit trees was about i to 

 0.3. The shade of apple trees reduces the intensity of the light, on an 

 average, from i to 0.234; the shade of pear trees from i to 0.233; that of 

 cherry trees from i to 0.345. 



For practical purposes, the lesson may be drawn from existing obser- 

 vations that the cultivation of fruit trees between field plantations, so widely 

 recommended, is unprofitable for northern regions. For southern countries, 

 in which an excess of light and heat may at times injure the plants, the 

 method will be advantageous. We find this theory confirmed by the fact 

 that in Italy the fields are divided by rows of mulberry and olive trees, as 

 well as by grapevines. According to Linsbauer^ the cultivation of grapes 

 in Italy (on pergolas) and in Austria (on low stakes) has been determined 

 by adaptation to the light conditions. In southern regions, thedonger dura- 

 tion of the sunshine permits the shading method of growth on arbors, while, 

 in northern countries, the shorter period of sunshine must be fully used. 



Like Frank-Schwarz, we reproduce illustrations of beech leaves from 

 vStahl's well-known studies on the structure of shade leaves. In Fig. 152' 

 may be seen a beech leaf grown in the sun, in Fig. 153, one grown in half 

 shade; and in Fig. 154, another matured in strong shadow. We see from 

 these how the leaf decreases in size with deficient illumination. The pali- 

 sade cells (pp) are formed in a less characteristic way, the spongy paren- 

 chyma (schp) becomes especially reduced and the vascular bundle cords 

 weaker ; a more feeble bud development is coordinated with the lesser leaf 

 development. 



The formation of the tissue, especially the differentiation in the paren- 

 chyma tissue^, depends upon the light intensity in the spring. Hesselman* 



1 Annales agronomique.s, Vol. VII, 189]; cit. v. Oven. 



2 "Wiesner, Lichtgenuss der Pflanzen. 1907. 



3 MacDougal, D. F., The Influence of Light and Darkness, etc.; cit. Bot. 

 Centralbl. 1903. Vol. XCII, p. 296. 



4 Hesselmann. H., Zur Kenntnis des Pflanzenlebens schwedischer Laubwiesen. 

 Beih. Bot. Centralbl. Vol. 17, 1904, p. 311. 



