For many years it has been an open question whether the Mendelian type of heredity applied to crosses between distinct species, or only to crosses within a species, or between hybrid forms. To throw light on this point, W.R. Dykes made a number of hybridizations, and describes the result in the Gardeners' Chronicle of London (Vol. LVIII, pp. 196-197). With numerous pairs of characters, the results showed no dominance but only blending.
Iris boissieri, bulbous, with the beard of the sepals in the form of long straggling golden hairs 0.117 to 0.234 inch in length, crossed with I. tingitana having no trace of hair gave a hybrid with hair distinctly visible to the naked eye but less than 0.0585 inch in length.
I. tectorum (which has a tuft in place of hair) crossed with I. cengialtii (a hairy type) gave a hybrid with a light violet coloured tuft bearing a short hair.
I. xiphium (without perianth tube) crossed with I. tingitana and I. filifolia (having perianth tubes 0.975 and 0.507 inch, respectively) gave hybrids with perianth tubes respectively 0.507 and 0.234 inch long.
I. clarkei with solid stems crossed with I. chrysographes with the internal cavity of the stem occupying about half the diameter, gave a hybrid intermediate with central hollow almost but not entirely closed with pith.
I. pallida with papery spathes which become entirely white and dry before protruding from the floral opening, crossed with I. variegata with green and herbaceous spathes gave a hybrid with spathes green in the lower portion and parchment-like in the upper portion.
The hybrid between I. reticulata and I. bakeriana is intermediate between the parents as regards leaf shape.
Also with regard to the coloring of the petals many hybrids are intermediate between the parents of various species, e.g., I. pallida x I. variegata; I. trojana x I. variegata; I. boissieri x I. juncea; I. fulva x I. foliosa; I. forresti x I. sibirica.
With the exception of I. chrysographes x I. forrestii and also possibly of I. pallida x I. variegata and of I. fulva x I. foliosa all the above hybrids were sterile both with respect to their own pollen and that of both parents. The two possible exceptions are cases in which the parents are somewhat related whilst the fertile hybrid has more definitely related parents.
Another interesting species-cross, which to some extent confirms the above conclusions, is reported by S. Mottet in the Revue Horticole of Paris (87, pp. 582-583). Iris pumila, a species which flowers early (beginning to end of April) with I. germanica, of which the earliest flowers appear about the middle of May, yielded numerous varieties flowering in the middle of May, thus enabling growers to have a continuous supply of iris for about three months. Mottet has given the new forms the horticultural name Iris interregna and describes them as intermediate between the two parent species not only in date of flowering but for height, leaves and dimensions. Miss Sturtevant adds that interregna flowers are often larger than those of either parent.
|Grace Sturtevant, one of the leading iris breeders in the United States. Some of our finest iris varieties owe their origin to her. Picture from USDA Yearbook, 1937.|