SECTIONAL TRANSACTIONS.— K. 393 



pJace. The linkages arise either as a result of pairing between non-homologous 

 chromosomes or possibly from an interchange of segments between chromosomes. 

 The study of these linkages is thus throwing a further intensive light on the process 

 of mutation and its relation to evolution. 



Dr. C. E. B. Bremekamp. — The Taxonornic Importance of the Mode of 

 Branching in Vascular Plants. 



As early as 1837 Brongniart showed that axillary shoots are found only in the 

 Spermatophytes, that the branches of the Equisetales are not axUlary, but inter- 

 axillary, and that the ramification of the Lycopodiales and Filicales is of the 

 dichotomous type. Subsequent taxonomists, however, did not pay much attention 

 to the mode of branching. Velenovsky, to whom the various types were well known, 

 lessened the value of the differences by a rather unfortunate endeavour to show 

 that the ramification of the Equisetales is only a modified dichotomy. He was 

 probably led astray by the preconceived opinion that the Equisetales, as an integral 

 part of the Pteridophytes, should have the same type of branching as the other classes 

 belonging to this group. Further development of our knowledge of the vascular plants 

 has shown, however, that the characters by which the Pteridophytes and the Spermato- 

 phytes were originally separated are not of such paramount importance as they seemed 

 to be, and that the differences between the various classes brought together in the 

 group of the Pteridophytes were rather underrated ; it is only conservatism which 

 maintains at the present moment the Pteridophytes as a separate group. 



The importance of the dichotomous type of branching as a special character of 

 the rUicales, Lycopodiales, Ophioglossales and Hydropterides, was somewhat obscured 

 by Schoute's discovery of the occurrence of this type of branching in the palm genus 

 Hyphaene. I could show, however, that the dichotomy of these palms, although quite 

 distinct from any type of lateral branching existing among the Spermatoph3'tes, is 

 nevertheless not identical with the dichotomy in the above-named groups. The fact 

 that axillary buds are present everywhere in these palms demonstrates the enormous 

 distance which separates them from these groups. 



Branching, however, is not only of importance in distinguishing some of the main 

 groups of the vascular plants, but also in characterising smaller groups, especially 

 among the Spermatophytes. It is well known that several families and genera show- 

 abnormal types of branching which can only be explained as axillary bj' the intro- 

 duction of the notion of concrescence. The interpretation of these types of branching 

 sometimes offers considerable difficulty ; for instance, in the Asclepiadace£e, where the 

 ' extra-axillary ' inflorescences usually arise between the orthostichies. In the 

 Solanace3 concrescence is also a phenomenon of general occurrence. This was over- 

 looked by Eichler when he drew the diagrams of their flowers. In these diagrams the 

 gynoecium is shown in an oblique position with regard to the plane of the main axis 

 and the bract. Eichler's bract, however, is in reality a bracteole, and one of his 

 bracteoles a leaf of the shoot which arises in the axil of the false bract and whose first 

 internode is united with the peduncle. The true bract lies below the false bract 

 and exactly between the latter and the second true bracteole, in such a position, there- 

 fore, that the plane of symmetry passes through its middle. 



Friday, August 2. 



Dr. E. P. Phillips.— 4 Brief Sketch of the Flora of the Environs of Pretoria. 



This deals only with the Dicotyledons which are represented by seventy-four 

 families, just over half of the known South African families of plants. A comparison 

 ia made of the leaf, flower and fruit characters of the species with an area in the south- 

 western region. The various growth forms in the flora are noted, and an analysis of 

 the species, genera and families given. A short note on the affinities of the Pretoria 

 flora concludes the paper. 



Miss E. M. Young. — Physiological and Cytological Studies in the Genus 

 Monascus. 



