RECENT ADVANCES IN SCIENCE 125 



shows many points of apparent similarity to that of geotropic 

 curvature. 



Ecology. — Apart from detailed accounts of the vegetation of 

 different areas, which are becoming somewhat too numerous to 

 be noted here, some ecological works of general interest have 

 recently appeared. Albert and Gabrielle Howard (Agric. Res. 

 Inst. Pusa, Bull. 52) have made a very elaborate study of soil 

 ventilation, from observations on the growth of Indian crops, 

 emphasising the importance of this factor in plant life, and the 

 necessity for taking into account the different needs of different 

 species in this respect. Stapledon (Ann. Bot. 30), from a study 

 of the weeds of farm land, lays stress on the importance of 

 investigating these on a statistical basis, and in the light of 

 the community as a whole ; his results show that the weed 

 communities are decidedly responsive to change in soil, are 

 different near the altitudinal limits of cultivation from those 

 on the same soils at lower elevations, and are influenced by 

 the crop under which they grow — this last due largely to the 

 husbandry associated with the various crops. 



In a valuable paper on the periodicity of freshwater algae, 

 Trauseau (Amer. Jonrn. Bot. 3) brings together many observa- 

 tions and draws interesting conclusions, some of which appear 

 to be novel, as, for instance, that the normal length of the 

 vegetative cycle in Spirogyra is an inverse function of the 

 surface area of the cells, also that the concentration of natural 

 waters at their maximum is so small in comparison with the 

 concentrations of the cell-sap as to make it very doubtful 

 whether it is of any significance in initiating reproduction. 



Willis (Phil. Trans. Roy. Soc. 106) calls attention to the 

 remarkably high proportion of endemic species in the flora of 

 Ceylon — over 800 species out of 3000, and 23 of the 324 genera 

 represented. Six families with seven species each are entirely 

 endemic ; four families with a total of 102 species have 91 of 

 them endemic ; and 14 families containing 435 species include 

 255 which are endemic. Over a hundred of the endemic species 

 are extremely rare, in some cases being represented only by 

 about a score of individuals on a mountain top. Dr. Willis 

 considers that the various features of occurrence of the Cin- 

 galese endemics form " an insuperable objection to the theory 

 of natural selection and adaptation." For instance, the local 

 species are the rarest, which should not be the case if they had 



