Abstract
1. Seven species of the genus Collinsia Nutt. had 7 bivalents, and one species had 21 bivalents at metaphase I; one species had a somatic chromosome number of 14. 2. Two species with sessile flowers had a relatively low mean number of chiasmata at metaphase I, and one species with sessile flowers as well as the species with distinctly pediceled flowers had a relatively high mean number of chiasmata per bivalent at the same stage. 3. One plant of C. solitaria had a pair of supernumerary chromosomes, the first such observation in the genus. 4. A working hypothesis of the relationship among the species and the probable course of speciation are presented.
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