550 SECTIONAL TRANSACTIONS.—K. 
Dr. H. HamsHaw THomas.—The nature and origin of the Stigma (10.45). 
The conventional view of the carpel is a purely subjective concept. An 
objective treatment of carpel morphology at once demands a provisional 
solution to the question of the origin of the stigma. ‘The suggestion that 
the evolution of the stigma preceded the inrolling of the carpellary leaf 
involves physiological improbability. In seeking a new explanation we 
need to know more of the structure of the stigma, and of the cells or tissues 
which conduct the pollen tubes to the micropyles. The existing information 
furnished by Capus, Guéguen, Juel, and others has been almost entirely ig- 
nored by English and German morphologists. ‘The stigma is only the upper 
termination of the “‘ conducting tissue ”’ of the style > (Capus). This tissue 
usually extends downwards as a definite band or bands on the ovary wall 
to the vicinity of the ovules; it appears to originate from papillate cells with 
specialised contents, but becomes much modified in certain families (e.g. 
Composite), especially in the style. In many cases the conducting tissue 
extends to the bottom of the gynzcium before entering the ovary, and it seems 
only possible to explain this on the assumption that the conducting tissue 
(and therefore the stigma) originated at the base of the ovary and later ex- 
tended upwards. The structure and development of the carpel and stigma in 
Alchemilla, Rhodotypus,and other members of the Rosacez supports this idea. 
On this assumption a picture of the evolution of the stigma and carpel 
can be drawn which is possible from both the morphological and physio- 
logical standpoints, the carpel wall representing two fused pteridospermous 
cupules. This view provides an explanation of what we know about the 
early stages of carpel development, of the vascular system of the carpel and 
of the anatropous ovule. We now know of fossil plants which exemplify 
most of the earlier stages in the supposed sequence of events. 
The angiospermous flower is not homologous with a vegetative bud, and 
it is quite possible that the Rosacez may be one of the more primitive 
families now living. 
Joint Discussion WITH Section A (Mathematical and Physical Sciences, 
q.v.) on The X-ray analysis of fibres (11.0). 
Alternative programme for Members not attending the above discussion :— 
Prof. H. S. HoLpeEnN.—On a new pteridosperm stem from Shore (11.5). 
The specimen described is a stem which has a markedly stellate outline 
in transverse section. There is a small homogeneous pith surrounded by 
primary xylem with mesarch protoxylem. The leaf-trace is mesarch and 
undivided. In common with the group of species described by Kubart, this 
stem forms a link between Lyginopteris and Heterangium. 
Prof. J. DoyLeE—The nature of heterospory (11.20). 
Dr. T. M. Harris.—On the reproductive organs of some early Bennettitales 
(11.40). 
Prof. R. A. FisHer, F.R.S.—The genetical system responsible for ever-sporting 
stocks (12.10). 
_ An outline of Winge’s theory of doubleness in stocks, and of its implica- 
tions, is given. 
A simple method of diagrammatic representation, applied to Miss Saunder’s 
data of 1911, shows both that the observed excess of doubles is due solely 
