CYTOLOGICAL DIFFERENTIATION IN GAILLARDIA PULCHELLA

Abstract

THE BLANKET FLOWER, a widespread composite of the southern United States, is morphologically and cytologically variable. No detailed studies of this species have been made, other than the taxonomic treatments by Rydberg (1915) and Biddulph (1944). Gaillardia pulchella has had a long and confused taxonomic history. It has been split into several distinct species by some workers (Rydberg, 1915; Nelson, 1926) and confused with the related Gaillardia aristata by others. METHODS.Eighteen collections of seed of Gaillardia pulchella (table 1) from different parts of the species range were grown in a standard habitat at the Indiana University experimental garden. Chromosome counts of these races were determined from microsporocyte and root-tip preparations. Morphological characters of these wild races and their artificially produced hybrids are given in fig. 1 and 2. Reciprocal hybrids between races were produced by bagging heads before the flowers opened, then transferring pollen to the fresh stigmas daily until all flowers had been pollinated. In the following discussion of hybrids, the formulae refer to both reciprocals. Mature embryos were cultured in order to facilitate germination. Embryos were limited in number, and the abnormal germination of some decreased their chances of survival under greenhouse conditions. No morphological differences were found in reciprocals, and the frequency of crossing in either direction was the same. In culturing embryos, Tottingham's modification of Knop's solution (Miller, 1938) was used in half the normal concentrotion with 1 per cent agar added. Achenes were sterilized in sodium hypoclorite (commercial Chlorox 1 part: distilled water 7 parts) for 1 hr., dissected, and embryos were planted vertically in 2.5 cc. of mineral agar in shell vials. Cotyledons began growth in two or three days, and seedlings were transplanted to 3-in. pots approximately four weeks later. When large enough, hybrids were transplanted to the garden. Hybrids which reached maturity grew much more vigorously and bloomed more profusely than either parent. They were morphologically intermediate in most respects, and 9 selected hybrids are evaluated in fig. 2. No character found in one parent clearly dominated the contrasting character in -the other parent. All hybrids were as tall or taller than