BOOK-NOTES, NEWS, ETC. 183 



responsible for their behaviour, but a combination of causes may 

 be acting, though in that case each cause must act mechanically 

 on all alike. The cause which seems the determining factor in dis- 

 persal is age within the country concerned. This opinion was based 

 upon the results of his work on the Ceylon flora, which showed 

 that the endemic species (presumably the youngest) occupied 

 much the smallest areas, those common to Ceylon and South India 

 (next youngest) areas considerably larger, and those of wider dis- 

 persal than this (the oldest) areas yet larger again, while at the 

 same time each group showed a graduated series of plants 

 occupying each size of area, the endemics varying down the scale 

 from 90 to 233, the wides up from 144 to 462. Not only do the 

 grand totals show this distribution according to age, but also 

 family by family, and genus by genus (of reasonable size) do so. 

 The rarity of all the endemics (in figures from 1 to 6) is 4-3, and 

 when taken in groups of not fewer than 14 it only varies from 3-9 

 to 4-9, while that of the other two groups varies similarly about 

 3-5 and 3-0. Some having objected that Ceylon is a special case, 

 he obtained confirmation of his views by working out the flora of 

 New Zealand. To test his hypothesis, he wrote the paper first 

 predicting what, under that hypothesis, must be expected, and as 

 all his predictions were confirmed by the facts, the result has 

 given him considerable confidence in the truth of the hypothesis. 

 One does not often come across cases like Ceylon, where the local 

 species can be divided into groups according to age, and confirma- 

 tion of his hypothesis must rest on finding cases to parallel one 

 or more of the features which showed so conspicuously in the 

 Ceylon flora. New Zealand parallels it in several respects, and 

 other cases are quoted in which similar parallelism is exhibited. 

 Some of the objections to these views were considered, e. g. the 

 hackneyed argument that introduced species spread rapidly over 

 islands at the expense of the indigenous flora ; this is shown by 

 the cases of Ceylon and Eio de Janeiro to be an unsound position. 

 The objection that the endemic species are the oldest in a country 

 was also dealt with, likewise that which asks why one does not see 

 the spreading going on, if it depend upon age. 



In upland regions of Japan there occurs in autumn a very 

 poisonous fungus growing on dead beech trunks and commonly 

 known by the name " Tsukiyo-take " — the moonlight fungus. 

 S. Kawamura in the Jourfial of the College of Science (Tokyo, 

 vol. XXXV, 1915) names the fungus Pleurotus japonicus ; it had 

 previously been called P. noctilucens by Inoko, but this name was 

 preoccupied and was moreover a nomen nudum. It is an 

 interesting fact that many of the luminous fungi belong to the 

 genus Pleurotus, though it is not commonly known that such 

 common species with us as Fojiies annosus and Polypoims 

 sul'phureus sometimes display luminosity, and the mycelium of 

 Armillaria mellea seems always to be luminous. Kawamura's 

 account gives full details of his investigation. The light is emitted 

 only by the gills, both hymenium and trama being luminous. 

 Luminosity is displayed over a range from about 5° C. to 40° C, 



