1. Ascherson, P. andGraebner, P. (1809).Synopsis der mitteleuropäischen Flora, II, Abt. l. Leipzig.
2. Buxton, B. H. andNewton, W. C. F. (1928). “Hybrids ofDigitalis ambigua andDigitalis purpurea, their fertility and cytology.”Journ. Gen. XIX.
3. Church, G. L. (1929). “Meiotic phenomena in certain Gramineae.”Bot. Gaz. LXXXVII, LXXXVIII.
4. Clark, C. F. (1910). “Variation and correlation in Timothy.”Cornell Agr. Exp. Stn. Bull. No. 279.
5. Darlington, C. D. (1929). “Chromosome behaviour and structural hybridity in the Tradescantiae.”Journ. Gen. XXI.