726 ^ TRANSACTIONS OP SECTION K. 



cylindrica) ; Miss T. L. Prankerd {Simplified Method for Estimating the 

 Strength of Wheat); Mr. W. Robinson {Germ-tuhes of Uredineae and Abnormal 

 Sperrjiogonia) ; Mrs. M. G. Thoday {Seeds of Gnetumgnemon) ; Dr. D. Thoday 

 {Micro-eudiometer for measuring gas evolved by assimdating water-plants) ; Mr. 

 H. B. Speakman {Branching of Rhizome in Selaginella Lyallii), and Professor 

 F. E. Weiss. 



FRIDAY, SEPTEMBER 10. 

 The following Papers were read : — 



1. The Phyletic Arrangement of the Filicales, with special regard to the 

 Dipterids and Pteridecz. By Professor F. 0. Bower, F.R.S. 



2. Further Deductions from the Figures of Rarity of the Ceylon Flora. 



By Dr. J. C. Willis. 



In a recent paper the author endeavoured to prove that the commonness of a 

 species depends upon its age (in the country concerned) and that local endemic 

 species are simply new species in the earlier stages of spreading. Accepting 

 these conclusions, we may go on to deduce many others from the figures of rarity 

 of the Ceylon tiora. 



From the fact that the species of wide distribution (which must be the 

 oldest) increase in number up the scale of commonness, whilst the endemics 

 (the youngest) increase downwards, and the 6eylon-Peninsular-Indian species 

 are comparatively evenly distributed along it, the conclusion is drawn that 

 tables like these represent three stages in the history of a group of species, the 

 distribution of the ' wides ' being the latest. 



Tables, &c., were given from which it is concluded (1) that there is no 

 evidence that any species are dying out ; (2) that the dry zone of Ceylon was on 

 the whole peopled with plants a good deal later than the wet, and received its 

 flora in two ways, either directly from the dry zone of India, or from the wet 

 zone of Ceylon, the plants entering by the latter route becoming more quickly 

 common ; and (3) that there is little to choose in average age in Ceylon between 

 {a) herbs and (6) shrubs and trees, though there is evidence to show that the 

 Monocotyledonous trees and shrubs are very old, and that the Gamopetalse as a 

 whole are older in Ceylon than the Archichlamydeae. 



3. The Periodicity , due to Coppicing, exhibited by the Ground Flora of 

 Oak-Hornbeam Woods on Clays and Loams. By Dr. E. J. 

 Salisbury. 



Before the shrub layer is cofipiced two phases can be recognised, viz., (1) 

 The Light Phase, extending from the leaf-fall in autumn to leaf -expansion in 

 spring, and (2) the Shade Phase, from about the middle of spring to autumn. 

 During the former period from 40 to 60 per cent, of the total light reaches the 

 ground vegetation, whilst during the latter from 5 to under 1 per cent, only 

 penetrates. It is probably the degree of shading during the Light Phase which 

 largely determines the amount of ground flora. (The light intensities were 

 obtained by means of an actinometer. The intensity outside the wood at the 

 time of the test being taken as the standard.) The alternations between 'Light ' 

 and ' Shade ' phases also correspond to alternations in the degree of exposure. 

 The ground-flora of the uncoppiced wood consists almost exclusively of perennial 

 herbs which possess storage organs. These produce their foliage very early in 

 the spring. Thus most of their assimilation is carried on duiing the ' Light ' 

 phase. With a few exceptions {Mercurialis, Galeobdolon) the vegetative periods 

 of the members of the shade-flora end soon after the ' Shade ' phase begins. 



After the undergrowth is coppiced there is a great increase in the number 



