270 SUMMARY OF CURRENT RESEARCHES RELATING TO 



Absorptive and Diffusive Power of Leaves.* — The following are 

 the chief conclusions on these subjects arrived at by P. Maquenne : — ■ 



1. All leaves disperse a portion of the heat they receive. If the 

 Bourbouze light is used for this purpose, about 25 per cent, of the 

 entire heat is dispersed ; but with Leslie's cube only a small per- 

 centage. 



2. The two sides of the leaves behave differently, the under side 

 usually 'dispersing more light than the upper side ; though sometimes 

 the reverse was observed. 



3. The leaves absorb a large portion of the heat of a Bourbouze 

 lamp ; this absorption depending on the water, clilorophyll, &c., con- 

 tained in the leaves, and on diffusion at the surface of the cells. The 

 upper side of the leaves absorb more heat than the under side. 



4. Thick leaves are more absorbent than thin leaves. 



5. The dark heat which radiates from boiling water is absorbed 

 nearly as completely as by ordinary blackened surfaces. 



6. Leaves allow the rays of heat to pass through them better the 

 younger and thinner they are. 



7. Leaves allow this heat to radiate almost as readily as lamp- 

 black. 



8. The absorptive power of chlorophyll for dark rays of heat 

 nearly equals that of water. 



Colouring Matters of Flowers.f — Professor J. B. Schnetzler, in a 

 paper on this subject, points out that hitherto it has generally been 

 supposed that the various colours observed in plants were due to so 

 many different matters, each colour being a different chemical com- 

 bination without relation to the others. He is able, however, to show 

 by experiment that when the colour of a flower has been isolated by 

 putting it in alcohol, all the colours which plants exhibit may be 

 obtained by adding an acid or an alkali. Plants of pseony, for example, 

 yield, when macerated in alcohol, a violet-red liquid. If some acid 

 oxalate of potash be added, the liquid becomes pure red ; while soda 

 changes it, according to the proportion used, into violet, blue, or green. 

 In the latter case, the green liquid appears red by reflected light, 

 just as a solution of chlorophyll does. The sepals of pseony, which 

 are green bordered with red, become wholly red when placed in a 

 solution of acid oxalate (binoxalate) of potassa. These changes of 

 colour, which may be obtained at will, may well be produced in the 

 plant by the same causes ; since, in all plants, there always exist acid 

 or alkaline matters. The transformation from green into red, observed 

 in the leaves of many plants in autumn, is due to the action of the 

 tannin which they contain, on the chlorophyll. Thus, without 

 desiring to af6.rm it absolutely, Professor Schnetzler supposes, a p-/on, 

 that there is in plants only one colouring matter, chlorophyll, which, 

 being modified by certain agents, furnishes all the tints that flowers 

 and leaves exhibit. 



* Maquenne, 'Eecherches sur la determination des pouvoirs absorbents et 

 diffusifti des feuilles,' Paris, 1880. See Bot. Centralbl., ii. (1881) p. 70. 



t Bull. Soc. Yaud. Sci. Nat., xvii. (1880) pp. 96-8. See 'Science,' i. (1880) 

 p. 30G. 



