During 1949 I learned a lesson about the pollination of rose blooms that had escaped me in fifteen years of work.
When I first attempted the cross pollination of hardy roses, in 1932, I wrapped a piece of paper over the emasculated and pollinated blooms, tying it on rather tightly below the hip with a string. It was many years before I discovered that if the string was pulled too tight and the circulation of air prevented inside the paper pocket, the results would be unfavorable. However, during these years I was sufficiently careless in making a tight wrap to secure abundant success with a large proportion of my crosses.
In 1947, shortly after my pollinations for the season were over, I heard a suggestion that appealed to me. It was to remove all petals and petaloids, also all sepals, for ease in finding the hip again from the flower, in order to leave no sign to the bees or other insects, make the pollination, and then leave the pollinated hip exposed to the sun and air, not only for the swelling and ripening period, but for the first day also.
So I had to try it. One of the specific crosses that I intended to make in quantity was chosen for the experiment, for which the lack of a tag was to be the identification mark. The same cross was also made according to my previous methods, though in smaller numbers, as a control or check. I found the labor involved in making pollinations greatly reduced by this simplified method, and I could make over twice as many in the same time by avoiding the labor of wrapping with paper, tying, and affixing the identification tags. It seemed a good idea at that date.
This year the papers used for wrapping were all cut as strips, so that even when folded and tied on tightly, the open slits at the sides provided plenty of ventilation.
When harvest time came, the difference in results was astounding. The hips that had been left uncovered failed more often, and those that did "catch" were small, with less than a dozen seeds usually. On the other hand, practically all those wrapped with paper "caught" successfully and made enormous hips, with between 50 and 80 seeds each. The rose-seed harvest of 1949 was thus one of the most generously rewarding I have ever had.
I can only suppose that shading the pollinated pistils from the sun results in the pollen more often getting its chance to operate than when the exposure is complete. At present there is no evidence to suggest that the same phenomenon might be observed in pollinations made in the greenhouse; however, I have a notion that there might be a similar but smaller gain to be secured by wrapping the pollinated flowers even though the pollinations are made under glass. The variety of rose that served as the mother parent in these tests was the well-known rugosa hybrid Hansa.