66o 



found that the plants, completing their development in a constantly reduced, 

 but not especially small amount of light, show a much scantier formation of 

 the assimilatory tissue than those specimens which have a good deal of light 

 in the spring but are strongly shaded in summer. With an equal amount 

 of leaf surface, plants grown in the sun, with their matured palisade paren- 

 chyma, transpire considerably more strongly than those grown in the shaded 

 According to Ricome"-, the palisade cells are said to be taller but narrower, 

 the vascular bundles more abundant in the petioles. The same difference is 

 found between specimens grown out of doors and in conservatories^. 



Investigations made by Count zu Leiningen* give us a satisfactory in- 

 sight into the amount of work performed by light and shade leaves. He 



Fig-. 152. Cross-section through a beech 



leaf matured in the sun. (After 



Stahl.) 



Fig. 153. Cross-section through 



a beech leaf from a half shaded 



position. (After Stahl.) 



Fig. 



154. Cross-section through a beech leaf from a very shady place. 

 (After Stahl.) 



pp palisade pareiich\ 



spoiijry parciichx 



found in the beech, reckoned on the same amount of leaf surface, a con- 

 siderably smaller content in pure ash (with the exception of silicic acid) in 

 sun leaves than in shade leaves ; the nitrogen content was corresponding. 

 We explain this condition of affairs as follows : — the root system provides 

 the leaves with equal amounts of mineral substances ; it now depends upon 



1 Bergen, J., Transpiration of sun leaves and shade leaves of Olea europaea 

 and other Orval-leaved evergreens. Bot. Gaz. Vol. 38, 1904, p. 285. 



-' Ricome, R.. Action de la lumifere sur des plantes 6tiol6es. Rev. gen. de Bot. 

 1902, t. XIV, p. 26. 



3 Klister, Review of "BM^lian, Influence de la culture en serre, etc.," in Holl- 

 rung's Jahresber. iiber Leistungen auf d. Geb. der Pflanzenkrank. Vol. VII, 1905, 

 p. 7. (Further notes on Sun and Shade Leaves, cf. Kuster, E., Pathologische Pflan- 

 zenanatomie 1903, p. 24, etc.) 



4 Leiningen, Wilhelm, Graf zu, Licht. und Schattenblatter der Buche. Naturw. 

 Zeitschr. f. Land- u. Forstwirtsch, 1905, III Year, Part 5. 



