SECTIONAL TRANSACTIONS.—K. 453 
The study of chromosomes furnishes fundamental evidence in the tracing of 
phylogenies. It should be recognised by taxonomists as an essential element in 
the discrimination of genera and species. 
(b) Dr. J. W. Hestop Harrison. 
(c) Prof. Moraan. 
(d) Mr. Junian Huxtey. 
(e) Miss K. Buacksurn. — Chromosomes and Classification in 
the Genera Rosa and Saliz. 
Rosa is unique in the extent of its polyploid series built up on a base number 
of seven chromosomes. ‘here is a first series with somatic counts of 14, 28, 42 
and 56 which halve normally at the reduction division. Among these is 
R. Wilsoni, a hexaploid mutant arising in a similar way to the tetraploid form 
of Primula Kewensis, This type of polyploidy is also found in Salix, but, 
contrary to the condition in fosa, has little systematic value, as it appears to 
have arisen separately in different sections, although probably also originating 
in hybridity. 
In Rosa there are other series in which the terms diploid and haploid are 
not strictly applicable, since only some of the chromosomes pair at the reduction- 
division. ‘here are two series, according to the number of chromosomes which 
pair. In the first of these, which comprises triploid, tetraploid, pentaploid, and 
hexaploid forms, seven chromosomes pair; and in the second, consisting of 
pentaploids and hexaploids, there are fourteen pairs. 
Thus we have in Rosa two types of tetraploid forms and three of hexaploid. 
That hybridity is really the cause of the whole series may be deduced by 
comparison with known hybrids such as Rosenberg’s Droseras, and also from 
a study of Rosa Wilsont. 
(f) Mr. A. D. Peacock. 
(g) Prof. Orro RosEnsere.—A Cytological Basis for the Pro- 
duction of Species by Hybridisation. 
The number of chromosomes in a pure species is a balanced, diploid one. 
In a hybrid between parents differing in number of chromosomes such a balanced 
chromosome-number can be acquired in one of two ways. If the difference is 
in number of sets of chromosomes, the result sometimes will be normal. hetero- 
typic divisions and constancy in chromosome-number by ‘allosyndese’ and 
“autosyndese.’ In other cases by non-disjunction some extra chromosomes are 
present in the germ cells. In the heterotypic division of a plant produced by 
the union of two such germ cells it can happen that the extra chromosomes are 
homologous and able to conjugate, and it follows that the chromosome-number 
of its offspring will be constant and higher than the original parental number. 
(h) Dr. E. C. Jerrrey.—Polyploidy and the Origin of Species. 
(i) Prof. W. P. Tuompson.—The Deficiency in the Number of 
Chromosomes in a Dwarf form of Wheat. 
(j) General Discussion. 
24, Prof. A. H. Hurcuinson.—The Age and Rate of Growth of British 
Columbia Trees in Relation to Ecological Factors. 
_. Graphs are given showing rate of growth as indicated by annual rings during 
the stages of youth, maturity, and old age under varying ecological conditions. 
_ The factors determining rate of growth frequently differ from those determining 
_ the age of maturity and decline. 
Afternoon Excursion to Holland River Sphagnum Marsh. 
