94 SUMMARY OF CURRENT RESEARCHES RELATING TO 



unclor uornuil conditions ? How much water must be present in tlio 

 soil ? And how is the proper quantity of water to be retained ? 

 Barley was sown in quartz sand, to which had been added sufficient 

 plant-food, and the amount of water present was GO per cent, of the 

 whole retainable water. The observations showed that the evapora- 

 tion was much more dependent on the temperature of the air than on 

 the evajiorating surfaces ; a rising tenii)erature with dryness increased 

 the evaporation, and vice versa. When the temperature remains con- 

 stant, then the moisture of the air greatly aftects the evaporation, 

 which may in dry air be raised to double, and in moist air reduced 

 to one-half that which is evaporated luider normal conditions ; but 

 this alteration has no effect on the physiological functions of the 

 plant so long as the condition of soil remains normal. A long 

 account of the construction of the ajiparatus used in the research is 

 given. The rapidity of the air-currents has much influence on the 

 evaporation, but the effect is much less than those exerted by warmth 

 and moisture. To observe the effect of light, two healthy and well- 

 grown barley plants were examined, the one under a bell-jar painted 

 white, the other under a clear glass jar, both of them connected with 

 the ventilating apparatus above referred to ; other coloured shades were 

 also employed, but all with a similar result, that light has a very 

 considerable influence, but not so great as that exercised by heat and 

 moisture. 



Experimenting with sunflowers, the author finds that the rise of 

 the sap is independent of the leaves, and that moisture is carried up 

 by the roots, so long as there is a certain degree of water in the soil ; 

 the minimum of moisture seems to be slightly above 8 per cent, of 

 the dried soil. 



Respiration of Plants.* — The second part of H. MoUer's paper on 

 this subject is devoted to intermolecular respiration. The method em- 

 ployed for measuring this is entirely the gasometric ; and the apj^aratus 

 used is described and figured. The observations were made on young 

 seedling plants of about ten species of flowering plants. The results 

 from the difterent plants were not uniform, the comparative intensity 

 of the normal and the molecular respiration differing in different 

 species, and apparently in the same plant under different conditions. 



Respiration of Tissues not containing Chlorophyll.f — G. Bonnier 

 and L. Mangin find their experiments on this subject generally con- 

 firm the results of those on fungi. But they have obtained some 

 important results respecting the variation of respiration during the 

 development of plants, and the constancy of the relationship between 

 the amounts of gas absorbed and evolved. The experiments were 

 made on roots, rhizomes, seeds, flowers, &c. 



Solar light, direct or diffused, diminishes the interchange of gases ; 

 while the intensity of respiration increases with the temperature. The 



* Ber. Deutsch. Bot. Gesell., ii. (1884) pp. 306-21 (2 pis.). Cf. this Journal, 

 iv. (1884) p. 921. 



t Aim. Sci. Nat., xviii. (1884) pp. 293-382 (2 pis.). See infra, p. 104 ; also 

 this Jouraal, iii. (1883) p. 39G. 



