434 SECTIONAL TRANSACTIONS.— K. 



examined cytologically, and differences in meiotic behaviour are demon- 

 strated by means of lantern slides. 



As far as possible herbarium specimens illustrating the different types 

 are exhibited. 



Mr. J. W. G. Lund. — The algcB of the margins of ponds (12.0). 



The nature of the substratum of the marginal regions of certain ponds is 

 largely dependent on the degree of exposure to which they are subjected. 

 Where strong wave action is absent vegetable detritus can accumulate. 

 This vegetable matter is deposited each autumn and consists mainly of 

 fallen leaves from nearby trees and the remains of aquatic plants. In such 

 regions planktonic, epiphytic and bottom-living algal communities occur. 

 These communities overlap somewhat. The bottom-living community 

 consists largely of motile forms, especially flagellates, and shows a seasonal 

 periodicity which can be correlated with the change taking place in the 

 vegetable detritus. This change consists in the breakdown of the vegetable 

 organic matter with the production of a mud rich in humus. The deposits 

 in the deeper regions of the ponds are of a different type and possess a flora 

 dominated by diatoms. The types of flora observed are probably generally 

 of the same nature in the littoral regions of most ponds and lakes. 



Afternoon. 

 Exhibits (2.15-5.0). 



Mr. C. G. Chesters, Mr. H. E. Croxall and Miss K. M. Keene. — 

 .Demonstration of cultures and preparations illustrating the 

 structure and development of the imperfect and perfect stages 

 of certain species of Diatrype, Eutypa, Diatrypella and Antho- 

 stoma. 



Dr. B. CoLSON. — Photomicrographs of fungi. 



Mr. A. D. Cotton. — A Cladophora ball from Ireland. 



Miss E. M. Debenham. — Stem apices of Selaginella arenicola 

 Underwood. 



Dr. J. W. Gregor. — Experimental taxonomy. 



Prof. T. M. Harris. — Naiadita, a strange fossil Bryophyte. 



Sir A. W. Hill, F.R.S. — Rhododendron adenopodum. 



Miss Joyce E. How. — Factors controlling the growth of Boletus 

 elegans on gelatin media. 



Dr. T. J. Jenkin and Dr. P. T. Thomas. — The breeding affinities 

 and cytology of Lolium perenne. 



Mr. J. W. G. Lund. — The algae of the margins of ponds. 



Dr. M. A. H. Tincker. — Growth - promoting substances and 

 horticulture. 



