Note 11 — Chapter I

A discussion of this subject with references to literature is given by Rolfe, in an excellent paper on "Hybridisation viewed from the standpoint of Systematic Botany" (Jour. R. Hort. Soc., XXIV, 1900, p. 197). He concludes: "The simple fact is that the two plants (L. diurna and vespertina) are thoroughly distinct in numerous particulars, and affect such different habitats that in some localities one or the other of them is completely wanting. But when their stations are adjacent they hybridise together very readily, and it is here that these intermediate forms occur which have puzzled botanists so much." The same paper contains valuable information concerning several cognate illustrations.