94 B exon-— Anatomy of Teratological Seedlings. II. 
fusion occurs only for a very short distance along the hypocotyl, to others in 
which it is so complete as to produce an apparently tetracotylous seedling. 
It must be pointed out, however, that the production of two or more 
distinct embryos may be accompanied by the splitting of one or more of 
them, as is shown in the Coniferae, and that when, as in the Animal Kingdom, 
twinning is known to be due to the separation of the two halves of a single 
embryo, fusion may be only partial. 
Whilst both suggested methods of ‘twinning’ seem possible the lack 
of evidence as to ovular conditions in Centranthus forbids any decision as to 
the actual mode of origin of the seedling under discussion. 
Summary. 
(t) The vascular anatomy of a number of Centranthus ruber seedlings 
showing all stages of polycotyly from hemitricotyly to tetracotyly 
is described. 
(2) These, whilst agreeing in broad outline with the types of structure found 
in Cheiranthus Cheiri, are found to differ in — 
(a) the frequency of fusions between cotyledons. 
(1 b ) the presence in some seedlings of a cotyledon the median 
bundle of which retains its collateral structure. The significance 
of these features is discussed. 
(3) The vascular anatomy of a ‘twinned’ seedling is described, the 
‘ twinning ’ being due to — - 
(a) the fusion of distinct embryos, or 
(b) the partial separation of the daughter-cells resulting from the 
quantitative division of the embryo initial. 
I am indebted to Professor J. W. Carr, University College, Notting- 
ham, who has granted every facility for the investigation, and also to 
Mr. H. S. Holden, University College, Nottingham, for his valuable help 
and criticism. 
Literature. 
1. Braun, A. : liber Polyembryonie und Keimung von Coelebogyne , ein Nachtiag zu der Ab- 
handlung liber Parthenogenesis bei Pflanzen. Abhandl. Konigl. Akad. Wiss. Berlin, 1859. 
2. Compton, R. H. : An Investigation of the Seedling Structure in Leguminosae. Jour. Linn. Soc. 
(Bot.), 1912. 
3. : Syncotyly and Schizocotyly. Ann. Bot., 1913. 
4. Coulter, J. M., and Chamberlain, C. J. : Morphology of the Gymnosperms, 1916. 
5. Davey, A. J. : Seedling Anatomy of Certain Amentiferae. Ann. Bot., 1916. 
6. Hill, T. G., and de Fraine, E. : On the Seedling Structure of the Gymnosperms. I-IV. 
Ann. Bot., 1908-10. 
7. . : The Seedling Structure of Centrospermae. Ann. Bot., 1912, 
8. Hofmeister, W. : Flora, 1857. 
9. Holden, PI. S., and Bexon, D. ; On the Anatomy of some Polycotylous Seedlings of Cheiranthus, 
Cheiri. Ann. Bot., 1918. 
10. de Vries, H. : Mutation Theory, vol. ii, 1911. 
