616 SECTIONAL TRANSACTIONS.— K. 



The question of relative sexuality as defined and illustrated for Ectocarpus siliculosus 

 by Hartmann has been reinvestigated, and his methods have been extended to other 

 members of the group. Data have been collected that add to knowledge of the 

 sexual reactions of the Ectocarpaceae. 



The facts relative to Ectocarpus siliculosus serve as a basis for the wider discussion 

 of the factors underlying unequal numerical occurrence of sexual and asexual 

 generations of algse in general. The question of the relations between reproductive 

 phase and geographical distribution is raised. 



Afternoon. 



Prof. A. C. Seward, F.R.S. — An Exhibition of Reconstructions of the 

 Vegetation of Past Ages. 



Mr. T. M. Harris. — A Petrified Plant from the Devonian of Australia. 



Description of the well-preserved leafless axes of a Psilophytalean Plant. The axis 

 consists of a broad cortex of three zones and a star-shaped stele composed of a mass 

 of tracheids surrounded by a little phloem. The xylem consists of an inner mass of 

 irregularly arranged tracheids, outside which is a protoxylem, and in some stems a 

 pecuHar sort of secondary wood. The tracheids of the protoxylem have scalariform 

 pits ; those of the metaxylem have multiseriate bordered pits. 



The plant is considered to be intermediate between Asteroxylon and Cladoxylon. 



Prof. Y. Ogura. — Some Japanese Mesozoic Plants. 



Prof. F. E. Weiss, F.R.S. — The Genetics of a Tropeolum mutant. 



The mutant in question was a specimen of Tropeolum, which, in place of the normal 

 peltate leaves, bore spathulate leaves often with a pitcher-like formation at the base, 

 which looked as if the normal development of the peltate leaf had been arrested on the 

 adaxial side while the apical portion of the leaf had undergone considerable elongation. 

 Nearer the apex of the shoot the leaves subtending the flowers showed very little of 

 the ascidium formation and were almost spathulate. Compared with the normal 

 foliage of Tropeolum the leafstalks were comparatively short and possessed no 

 sensitiveness to contact. Two further pecuharities occurred in the flowers. Firstly, 

 the hair-like fringes characteristic of the anterior petals of Tropeolum were either 

 completely absent or only represented by very few lateral outgrowths. Secondly, the 

 flowers proved to be sterile. The pollen was well developed and fertile, but flowers 

 when self-pollinated or crossed, though the ovary underwent some development, 

 produced no fertile seeds. The mutation seemed therefore to afiect not only the 

 vegetative leaves but also certain leaves of the flower, namely, the anterior petals 

 and the carpels. Since the pollen seemed to be normal, it was used to polUnate a 

 normal form with difierently coloured flowers and was found to be quite fertile, a 

 number of seeds being obtained. In the f^ generation all plants produced normal 

 leaves, had fringed petals and produced fertile seeds, so that the mutation seemed to 

 be definitely recessive. In the next (f ^) generation Mendelian segregation took place, 

 the three characters showing themselves definitely linked. The mutation was not 

 linked with flower colour. The recessive form showed the recessive leaf-form from 

 the seedling stage, the flrst leaves being spathulate and very different from the 

 partially peltate seed leaves of the normal Nasturtium. It was noticeable, however, 

 that several of the recessive seedhngs showed a tendency to outgrow more or less in 

 the further course of their development the abnormal leaf -form, and produced almost 

 peltate leaves. One of these, which was used for further experiment, proved to be 

 partially fertile, so that, with the diminution of the extent of the mutation, the latter 

 showed itself in both the vegetative and floral organs. The offspring of these forms 

 always showed the abnormal leaf-form in their first leaves, but the further leaves 

 showed the mutational character less strongly, some becoming almost peltate. 

 Towards the end of the season, however, the more spathulate leaves again made their 

 appearance in the small leaves subtending the flowers. The interest, therefore, of 

 this mutation lies firstly in the linkage of characters in three different organs, and 

 secondly in the fact that in some of the extracted recessives the factor causing or 



