Physiologie. b'-'D 



GRIFFON, Ed., Recherches sur l'assimilation Chloro- 

 phyll i e n n e des ieuilles dont on eclaire soit I a 

 face superieure, soit la face inferieure. (Comptes 

 rendus de l'Academie des Sciences de Paris. 4 aoüt. 1902.) 



Les feuilles sont placees dans des eprouvettes aplaties dont 

 une face est noircie; de cette facon l'on peut exposer ä la 

 lumiere l'une ou l'autre face des feuilles et les gaz trouvent les 

 memes voies d'entree et de sortie. 



Avec une feuille ä mesophylle heterogene dissymetrique, 

 l'assimilation baisse toujours, si c'est la face inferieure qui reeoit 

 la lumiere au lieu de la face superieure. Les differences varient 

 suivant les especes. Le maximum se trouve pour les feuilles 

 epaisses ä parenchyme bien heterogene : Troene du Japon 

 (100 ä 54), Laurier-cerise (100 ä 48); le minimum pour les 

 feuilles minces d'Erable plane (100 ä 88), et avec le Bambou 

 (100 ä 92); la moyenne avec le Lilas (100 ä 68), le Dahiia 

 (100 ä 75), le Framboisier, le Tilleul argente (100 ä 68). Le 

 plus grand e'cart a ete obtenu avec 1' Eleagnus argentea (100 

 ä 36). Pour des feuilles placees dans les conditions naturelles, 

 une face exposee ä la lumiere directe du soleil, l'autre ä la 

 lumiere diffuse, l'ecart le plus grand a ete de 100 ä 88. 



Bonnier. 



HEDGCOCK, üeorge G., The relation of the Watrr Content 

 of theSoil toCertain Plants principally Mesophyt vs. 

 (Studies in the Vegetation of the State; II. University of 

 Nebraska Botanical Survey of Nebraska. VI. 1902. p. 1— 79.) 



This paper is based on the experimental study of the 

 conditions influencing the growth of plants in different soils, 

 the water content of such soils, the relative amount of the 

 water in the plant and in the soils and how the limit of 

 physiological water is affected, with a statement as to the 

 influence of drought on plants. 



The amount of physical water in soils the author states 

 varies directly with their water-retaining capacity, while the 

 amount of physiological water varies directly with the amount 

 of physical water held in the soil and inversely with the amount 

 of hygroscopic water. The amount of water in the soil non- 

 available for the use of the plant is dependent directly upon 

 the ability of the plant to withdraw water from the soil, and 

 this ability is affected by soil composition and soil texture. 



The percent of water in the tissues of the plant is usuallv 

 the greatest in seedlings, and decreases gradurlly a; the plant 

 grows older. When first wilting, Mesophytes apparently lose 

 water in almost the same ratio by weight as the soil ; Hydro- 

 phytes probably lose weight more rapidly than the soil, while 

 Xerophytes lose weight very slowly when subjected to drought. 

 As respects dying plants, seedlings die with a greater percent 

 of water in their tissue than older plants; mature plants contain a 



