SECTIONAL TRANSACTIONS— K. 507 



Dr. J. B. Simpson.— Fossil pollen of dicotyledons of Jurassic age. 



Mr. K. V. Srinath. — Nutrition of embryo sac in Calceolaria. 



Sub-Department of Plant Physiology, Botany School, Cam- 

 bridge. — Apparatus. 



Dr. H. Hamshaw Thomas, F.R.S.— The works of Richard Bradley, 

 the first professor of botany in Cambridge, 1724-1732. 



Dr. H. Hamshaw Thomas, F.R.S., and Mr. H. Andrews — 

 Pachyderphyllum and Sarcostrobus, Jurassic plant remains of 

 problematical affinities. 



Miss P. E. Thomas. — Monoblepharidales. 



Mr. T. G. Tutin.— (a) The flora of Lake Titicaca ; {b) Species of 

 Hydrodictyon from Peru. 



Dr. E. F. Warburg. — British forms of Sorbus. 



Mr. P. Warnock. — Parasitic fungi on Rosa. 



Dr. A. S. Watt. — The morphology of the bracken. 



Dr. D. H. Valentine. Forms of Viola silvestris and Viola Riviniana 

 and of the hybrid between them. 



Material illustrating virus diseases of plants exhibited throughout 

 the meeting by : — 



Dr. R. N. Salaman, F.R.S., in the Potato Virus Research 

 Station. 



Dr. Kenneth M. Smith, in the Potato Virus Research Station. 



Mr. N. W. Pirie and Mr. F. C. Bawden, in the Sir William 

 Dunn Institute, School of Biochemistry. 



Wednesday, August 24. 



Dr. E. F. Warburg. — The origin and distribution of the British forms of 

 Sorbus (lo.o). 

 Three diploid species (n = 17) occur in Britain, S. Aucuparia widespread 

 over the whole, S. torminalis in England only where it is widespread but 

 local, and S. Aria ranging from Kent to the Wye Valley and the Mendips. 

 Hybrids of S. Aria with each of the other species occur. The remaining 

 British forms are triploid or tetraploid. They may be divided into three 

 groups as follows : A — species allied to S. Aria, B — species intermediate 

 between A and 5. Aucuparia, C — species intermediate between A and S. 

 torminalis. These species are mostly confined to small areas on the lirne- 

 stone in the West and North, where they entirely replace S. Aria, with 

 which they grow only in the Wye Valley and in Somerset. They are all 

 apparently endemic except for S. rupicola, the most widespread in Britain 

 which also occurs in Scandinavia, and possibly for 5. porrigens. Some of 

 these forms are almost certainly apomictic. Groups B and C are presumed 



