Mem. Hort. Soc. N.Y. (1927)
Sterility Encountered in Rose Breeding
J. H. Nicolas

The garden roses of today are so highly hybridized, many representing a succession of selected selfings, that a large percentage have run their course of fertility. Some are sterile with one pollen of proved potency and fertile with another. Although the pigmentation of two prospective parents may not have direct influence on fertility, yet I have observed that the more extreme the combinations the less successful I was in obtaining fertility. As an example Hawlmark Crimson, a blackish crimson, is sterile both ways when crossed with a deep yellow, and also is R. Moyesii.