422 SECTIONAL TRANSACTIONS.— K. 



(3) difference in reaction by different plasms on the same genotype 

 (permanent or transitory) (Sirks, Vicia Faba and Phaseolus ; Lehmann, 

 Epilobium ; Schlosser, tomatoes) ; 



(4) elimination of zygotes or gametes of definite genotypical constitution 

 under influence of the plasm (Sirks, Vicia Faba ; Bateson, Chittenden, 

 Gairdner and Pellew, flax ; Skalinska, Aquilegium). 



A further problem is the question if the plasmatic nature can be changed 

 by the genotype or not ; though the majority of studies point to the negative 

 answer, this problem is still unsettled. 



Dr. S. Williams. — An examination of the evidence used in phylogenetic 

 problems (12.15). 



The evidence used in the quest of Phyletic Lines may be classified under 

 the heads of (a) the comparative morphology of living plants, (6) taxonomy, 

 (c) the comparative morphology of fossil plants, {d) the historical record 

 afforded by the fossils, and (e) plant distribution. To these there may be 

 added lines of research which, so far, have yielded relatively few data 

 relevant to phylogenetic problems, viz., experimental morphology (including 

 certain aspects of autecology), statistical studies, and cytogenetics. 



The validity of this evidence, apart from the historical record of the fossils, 

 has been repeatedly called in question. The validity of the evidence from 

 the fossil record is, however, generally accepted, but the fragmentary nature 

 of it has been repeatedly stressed. Few critics have gone so far as Lotsy 

 who, in 1916, stated that ' Phylogeny .... is no science, but a product of 

 fantastic speculations,' but many have adopted a less extreme although still 

 critical attitude. On the other hand, many morphologists have maintained, 

 or have returned to, a belief in the validity of the evidence taken as a whole. 

 All will agree that the phyletic problem still exists. 



The major problem is clearly as to whether the canons of comparative 

 morphology, as applied to living plants, to the fossils, or to cytological facts, 

 are scientifically sound and likely to lead to conclusions possessing a reason- 

 able degree of probability. The fossil record provides a useful, though 

 usually inadequate, check on the results derived from comparative methods. 

 An extremely important question is as to whether cytogenetics can be de- 

 veloped as a test in broad phyletic problems, thus extending the useful 

 results already attained in relation to the more limited, but cognate, problem 

 presented by the interrelationships existing within small taxonomic groups. 



A general discussion of the present position of phyletic morphology, 

 contributed to by specialists in the various fields of research mentioned 

 above, might prove of great value in defining the modern attitude to 

 Phylogeny and in indicating fruitful lines for future research. 



Afternoon. 

 Excursion to Gotham and the West Leake hills. 



Friday, September 3. 



Joint Symposium with Section D on Recent work in genetics and cytology 

 (a non-technical presentation designed in particular to interest those 

 not working on cytology or genetics). (lo.o.) 



Chairman : Prof. F. A. E. Crew. 



