4i 8 SECTIONAL TRANSACTIONS.— K. 



valid. Impulses pass along the flagellum from the base to the tip and the 

 organism is driven in the opposite direction. If the flagellum were held out 

 in a more or less extended position the organism would be driven backwards, 

 but in each of the organisms studied the flagellum is bent so that the im- 

 pulses supply a forward component. Hence the organism is driven 

 forward. 



Afternoon. 



Mr. G. E. Smith. — A developmental study of the epidermis (2.15). 



A number of obscure points in leaf development as a whole having been 

 encountered during a previous investigation, the elucidation of certain of 

 them was attempted. 



Some aspects of the developmental history of the epidermis form the 

 subject of the present communication, including : 



(a) The time of appearance of stomatal initials. 



(b) Regular and irregular division of the epidermal cells. 



(c) ' Epidermal mother cells.' 



(d) Development of irregular outline of cells. 



(e) The development of the epidermis of cotyledons and adult leaves of 

 the same plant. 



(/) Some references to the developmental state of the epidermis at the 

 time of food absorption through it in endospermic seeds, at germina- 

 tion. 



Dr. M. M. Richardson. — Structural hybridity and species differentiation in 

 Lilium. 



The concept that most ' Undefined hybrids ' are ' Structural hybrids ' is 

 shown to be true in Lilium Martagon album X L. Hansonii where a reduced 

 chiasma frequency and occasional failure of pairing of homologous chromo- 

 somes are associated with structural change. Lilium Martagon album X L. 

 Hansonii is heterozygous for six inversions whose positions at a particular 

 locus in particular chromosomes have been determined. 



The effects of crossing-over in structurally dissimilar bivalents are 

 discussed according to the Neo-Chiasmatype theory of crossing-over. 

 Expected behaviour is considered (a) for all kinds of structural change and 

 their relation to the centromere, (b) for the different kinds of crossing-over 

 in the dislocated segment, (c) the relation of such cross-overs to crossing- 

 over in other parts of the bivalent. It is only by a fully correlated knowledge 

 of the form and separation of bivalents at both the first and second meiotic 

 divisions, and thereby of new chromatid structures, that we can analyse 

 the exact nature and position of the structural change. 



Crossing-over occurs distally and proximally to the inversion as well as in 

 it. Double crossing-over in an inversion is also shown to have taken place 

 in another species of Lilium. 



This investigation gives a method for the analysis of the causes underlying 

 the failure of pairing which characterise species hybrids, and shows the 

 significance of structural change in the formation of species. 



Mr. S. Ramanujam. — Chromosome studies in the Oryzece (3.5). 



The Oryzeae with their primitive and advanced characters have long 

 presented difficulties to taxonomists in regard to their classification and 

 relative position in the family. 



