RECENT ADVANCES IN SCIENCE 47 



organic matter is abundant, combined with lack of bases. 

 Probably scarcity and abundance of nitrates determine 

 respectively the occurrence of C. minor and C. alba. 



Reed swamps, chiefly composed of Phragmites and Scirpus, 

 are found in stable situations that are sheltered with from 

 30-60% of organic material. The former extends to a 

 depth of 0*92 m. and the latter to 1*3 m. Where the mud 

 contains abundant silt and decay is rapid, Typha latifolia 

 becomes dominant. 



In areas which are exposed and where there is over 60% 

 of organic material, a society is formed of various species of 

 Sedge. 



Under conditions of relatively rapid inorganic sedimenta- 

 tion, the successive dominants are : Naias flexilis, Potamogeton 

 pusillus, etc., Nitella flexilis, Sparganium minimum, Castalia 

 alba, Phragmites, and Scirpus. This succession shows a pro- 

 gressive increase in organic material and decrease in depth. 



In the same journal Mr. Tansley describes experiments 

 on the relation as to soil conditions between the calcicolous 

 Galium sylvestre and the calcifugous Galium saxatile. It 

 appears that both can establish and maintain themselves on 

 either peaty or chalky soil, but that the rampant Heath Bed- 

 straw is heavily handicapped when growing on a calcareous 

 soil, and that the converse also is true. On chalk, G. saxatile 

 tends to become chlorotic and die, and the percentage of 

 germination is lower than on acid peat. Competition between 

 the two species appears to be effective through the direct 

 effect of the more vigorous growth of one species on its appro- 

 priate soil. 



In the Journal of Agricultural Research (Oct. 191 7), H. L. 

 Shantz and R. L. Piemeisel contribute an account of the 

 Fungus Fairy Rings of Eastern Colorado and their effect on 

 vegetation. This covers some 55 pages, and is profusely 

 illustrated with nearly 50 photographic reproductions and a 

 number of text figures. 



Three types are recognised, viz. those caused by Agaricus 

 tabularis as a result of which the vegetation is either killed 

 or badly damaged ; those caused by Clavatia, Catastoma, 

 Ly coper don, Marasmius, etc., in which the vegetation is 

 stimulated ; and those caused by Lepiota species which pro- 

 duce no visible effect. A typical ring formed by A. tabularis 



