RECENT ADVANCES IN SCIENCE 199 



Browne finds that the cones show progressive reduction, with 

 respect to the xylem, which is least in E. arvense and most 

 pronounced in E. limosum. 



Ecology. — Several interesting papers dealing with the 

 relation of plant growth to acidity have recently appeared. 

 Latter and Mcllvaine find that the hydroxyl ion is more 

 harmful than the hydrogen ion in equivalent concentration, 

 and that for germination a slightly acid reaction appears to 

 be most favourable. The plants studied were Wheat, 

 Glycine, Zea, Medicago saliva, and Trifolium. Of these the 

 maximum growth was obtained at Ph 5*94, a reaction of approxi- 

 mate neutrality being slightly less favourable for Medicago, 

 and markedly so for Wheat, Zea, and Glycine {J. Agric. Res., 

 1920). Hoagland had previously noted that the absorption 

 of NO3, Ca, and P04, was greater under slightly acid conditions 

 (Ph 5-5' 5) than when the solution was nearly neutral. The 

 Lime factor in permanent soil improvement is the subject 

 of two papers by Lipman and Blair {Soil Science, 1920). These 

 authors found that, on arable land without Leguminous plants, 

 in rotation, there was a loss of Nitrogen from the limed plots 

 as compared with the unlimed. They suggest a slightly acid 

 reaction on light and medium soils may be desirable to prevent 

 too rapid oxidation of organic matter. In the second paper, 

 treating of rotations with Leguminous crops, it is suggested 

 that the marked value of lime is to render the conditions 

 favourable for nitrogen-fixing organisms, since when Leguminous 

 plants are present, the gain from liming is pronounced. 



Brenchley {Ann. Applied Biol.) finds that the effect of 

 crowding on Barley plants, grown separately in water-culture 

 solutions, is at first beneficial, but subsequently deleterious, 

 tending to lower the amount of dry matter formed, and to en- 

 courage shoot development at the expense of the growth of 

 the root. Moreover, the consumption of nitrogen per unit 

 of dry matter is greater than in widely spaced plants. 



Cryptogams. — A useful summary of the recent literature 

 dealing with the sexuality of the Mucorineae is contributed by 

 Namyslowski to the Revue gmerale de Botanique. The con- 

 clusion is arrived at that external conditions greatly influence 

 the mode of reproduction, carbohydrates favouring the pro- 

 duction of zygospores, whilst organic nitrogenous materials 

 favour vegetative reproduction. Although normally monoe- 

 cious or dioecious, the latter is not a constant character, but 

 monoecious (homothallic) forms have been observed to arise 

 from dioecious (heterothallic), and in addition partially monoe- 

 cious or partially dioecious types have been recognised. 



The Mycoplasm Theory of Eriksson as applied to Puccinia 

 malvacearum has been the subject of experimental investiga- 



