1. Avery, P. (1930). “Cytological studies of five interspecific hybrids ofCrepis leonto- dontoides.”Univ. Cal. Pub. Agric. Sci. vi, 135.
2. Belling, J. (1928). “A working hypothesis for segmentai interchange between homologous chromosomes in flowering plants.”Univ. Cal. Pub. Bot. xiv.
3. Darlington, C. D. (1926). “Chromosome studies in the Scilleae.”J. Genet. xvi, 237.
4. — (1929). “Chromosome behaviour and structural hybridity in theTrades- cantiae.”Ibid. xxi, 207.
5. - (1930). “Chromosome studies in Fritillaria, III.”Cytologia, iii.