RECENT ADVANCES IN SCIENCE 225 



B. Davisii, when " selfed " yields singles only, but when the 

 pollen of this species is employed for crossing with doubles, 

 all the offspring have double flowers. The conclusion seems 

 justified that the male flower alone carries the double 

 character. 



Ecology. — The ecology of tropical rain forest forms the 

 subject of a paper by R. C. McLean in the current number of 

 the Journal of Ecology. The author finds that, as might be 

 expected from corresponding data from temperate woodlands, 

 the air among the bushes of the undergrowth exhibits consider- 

 able stagnancy with an almost uniform humidity for periods 

 of several hours, or even days. Here, too, the temperature 

 was found to be very uniform with an average of about 20 C. 

 Experiments with detached leaves of several different species 

 showed a maximum transpiration of only 0*4 of the evapora- 

 tion from a free water surface ; estimations of the air-space in 

 leaves of the shade plants showed this to be greater, per unit 

 of weight, than in the sun leaves ; also the number of stomata 

 per unit area was smaller in the former than in the latter. 

 The shade species, however, showed the higher mineral con- 

 tent. The author concludes from these results that the absorp- 

 tion of mineral salts is independent of the low foliar evapora- 

 tion, and suggests that a slow water-current may be maintained 

 by root-pressure accompanied by liquid excretion. 



J. Gray and G. J. Peirce {American Jour. Bot.), having 

 studied the stomatal reactions of Barley, Wheat, Oats, and Rye» 

 by direct observation, conclude that the main factor deter- 

 mining the opening and closure of the stomata is illumina- 

 tion, though a minimum turgor is requisite for their action 

 The observations were made on living leaves still attached 

 to the plant, and the measurements showed that the maximum 

 aperture was attained under maximum illumination irrespective 

 of the high or low humidity. 



R. B. Harvey, in a short but interesting note (Bot. Gaz.), 

 describes the result of experiments which showed that ice 

 formation within the tissue of a leaf is considerably retarded 

 by the presence of wax or a dense covering of hairs. 



Having regard to the important r61e played by Algae in 

 colonising bare, exposed surfaces, their capacity for resisting 

 drougat is an important feature. Miss Bristol has in this 

 connexion made cultures of soil collected at Rothamsted 



