BOTANY. 277 



ature goes above 42 to 43.5°, the optimum lor tlic lupiue, tlie respira- 

 tion will be somewhat less than before and the vitality of the plants 

 also weakened. 



On the formation of carbon dioxid and absorption of oxygen 

 by detached leaves, Berthelot and (r, Andre {Ami. (Jliini. at 

 Fliy.s., srr. ;, :' (i^'^/), 2)p. :2!)3-33'.>). — The authors have made a study of 

 the changes taking place in detached leaves, whether due to chemical 

 oxidation, to biological causes, or the action of bacteria on the leaves. 

 These changes offer an evident connection between the gaseous 

 exchanges of the air and the plant, which characterizes plant respira- 

 tion, and by Avhich the substance of the leaves is returned to the soil 

 in binary compounds, as water and carbon dioxid, and the other prin- 

 ciples constituting the soil. Three species of ])lants were selected for 

 the experiments. Wheat, representing an annual plant, ([uickly drying 

 and losing its vitality; Scdum maximuiii., as a perennial with very thick 

 leaves, of great vitality and drying with difticulty in firdinary air; and 

 the hazel nut, or filbert {Coryhis avellana), as a ligneous plant whose 

 leaves oifer an entirely different structure from either of the preceding 

 and which are capable of ra[)id drying. The elementary composition 

 of each was determined before beginning, and in every set of experi- 

 ments the conditions were made identical. 



The experiments were divided into 2 groups: (1) those made at a 

 temperature of 100 to 110° C, resulting in the immediate destruction 

 of the vitality of the leaves and giving purely chemical results, and 

 (2) those conducted at normal temperatures assisted by the action of 

 the cells and their contents and exterior microorganisms. 



In the first group are given the series of experiments which were 

 conducted (1) in a current of hydrogen, the water and CO2 collected; 

 (2) the same in current of air; (3) leaves in water and tlie vessel con- 

 taining them traversed with an air current; and (4) wet loaves placed 

 in a vessel of oxygen and sealed. In the second group there were 2 

 series. The leaves of one series were dried over sulphuric acid under 

 a bell jar and in the other they were kept in a humid, saturated atmos- 

 phere, and aided by the action of the organic materials of the leaves 

 and various microorganisms. 



The results of the experiments in all cases, whether the change was 

 rapidly ujade at a high temperature or much slower at a aor- 

 mal one, show that there was a constant increase in the carbon dioxid 

 formed and the oxygen taken in. This latter is shown in several cases 

 by the increased quantity of water found in the final over the initial 

 analysis of the leaves. The volume of CO2 formed sometimes is 3 to 5 

 times the volume of the dry matter of the leaves or 2 or 3 times that of 

 the green leaf. It was found that the amount by weight of CO2 formed 

 varied greatly with the experiment and the kind of plant used. The 

 extremes of C0> given off were 0.*27 to 41 per cent for the dry matter of 



