SECTIONAL TRANSACTIONS.— K. 407 



seen in this species, which, under the influence of Eriophyid mites, produced intersexes. 

 Cuttings from such intersexes have yielded purely male and purely female shrubs. 

 In willow hybrids the excess of females is often very great, and in many cases 

 the males have never been detected or reared. This suggests a switch-over of the 

 heterogametic sex comparable with the results of my Lycia-Nyssia crosses in the 

 Lepidoptera. 



(c) Prof. H. Kniep. 



In the dioecious Phanerogams the sex-determination of the diplonts (megasporo- 

 phytes and microsporophytes) can be explained on a Mendelian basis. This view 

 is not contrary to the fact that alteration of the relative number of sexes or complete 

 change of one sex into the other one is possible by variation of external factors. Every 

 plant contains the potentialities of both sexes, its development depending on factors 

 called realisators, the effect of which is evidently to be influenced by the environment. 



Amongst the Cryptogams the Fucaceae may be compared with the Phanerogams 

 and the Metazoa concerning sex-determination. 



In the diploid phase of the dioecious Musci no sexual tendency is predominant ; 

 this is proved by the fact that the gametophytes produced by experiment are 

 monoecious. In the Liverworts, on the contrary, one case is established in which 

 the one sex predominates over the other one in the gametophytic state. 



Great differences regarding sex-differentiation and sex-determination exist in the 

 Thallophyta. Genot5'pically — and not genotypically — caused determination of sexes 

 is neither in connection with the phylogenetical development of plants nor with 

 the degree of differentiation of sexes. In the Volvocales, for instance, we find both 

 cases in closely related genera : Chlorogonium, Gonium, and Pandorina are isogamics 

 and show genotypical sex-separation. In the anisogamic Eudorina the sexes are 

 also determined genotypically, but not in the isogamic Stephanosphasra and the 

 oogamic Volvox. 



Hybridisation experiments render it possible to establish the nature of sex also 

 in cases in which other methods fail (TJstilago nuda). The homothallic and the 

 heterothallic states are not always so sharply separated as in the Mucorineae (Coprinus). 



((/) General Discussion. 



10a. Dr. R. T. Gunther. — The Herbal of Apuleius Barbarus. 



The drawings of plants in the manuscript Herbal of Apuleius Barbarus, known 

 as MS. Bodley 130, are believed to have been executed about the year 1100 in the 

 Abbey of Bury St. Edmunds, and must therefore be regarded as the earliest English 

 plant- drawings known. Two types of drawing are distinguishable : (a) Conventional 

 figures, crudely executed and coloured, which, from having been repeatedly recopied, 

 have lost all semblance to the plants which they are supposed to represent ; some 

 of these appear to preserve the Discoridean tradition of plant illustration, (6) Natura- 

 listic figures which have obviously been drawii direct from the living plant. 



The MS. has recently been reproduced in facsimile by Captain Spencer Churchill 

 for distribution to members of the Roxburghe Club. 



11. Mr. W. C. F. Newton and Miss C. Pellew. — Primula Ketvensis and 



its Derivatives. 



The original Primula Ktwensis was a sterile hybrid between P. floribunda Wall, 

 and P. verticillaia Forsk. The tetraploid P. Kewensis owes its origin to somatic 

 doubling of the chromosomes in branches of the sterile plant. Each chromosome is 

 thus represented twice, and as these identical chromosomes pair in the reduction 

 division the tetraploid hybrid breeds true. This plant is not an example of the 

 production of a tetraploid form as the direct result of hj'bridisation. 



Aberrant plants which have gained or lost a chromosome are occasionally produced, 

 and triploid plants have been produced by back-crosses. From these plants and 

 their offspring the effect of loss or gain of particular chromosomes, as well as of inter- 

 change between verticillata and floribunda chromosomes, can bo determined. 



12. Mr. C. D. Darlington. — On the Cytology of the Cherries. 



Sour-cherry seedlings have double the chromosome number found in sweet cherries, 

 while in hybrids between the two types various intermediate numbers occur. Of 



