The American Naturalist 49: 5-21 (January 1915)
Some Fundamental Morphological Objections to the Mutation Theory of De Vries

Seeds on horseradish and Lilium candidum
Prof. Edward C. Jeffrey

Physiological sterility is frequently due to entirely different causes than genetical lack of harmony, as for example in the horseradish or the potato (Solanum). In the former it has been found possible to bring about the formation of fertile seed by simply girdling the top of the subterranean storage region of the plant, so as to prevent the undue descent of assimilates. The common white lily, Lilium candidum, presents a similar condition, for here the setting of seed takes place only when the leafy flowering axis is severed from its bulb and kept in water. So far as I am aware, there have been no experiments as to the result of severing the continuity of the phloem (girdling), in relation to the restoration of seed production in the potato. The common yellow day lily (Hemerocallis) possibly presents a case similar to that of Lilium candidum, for it does not ordinarily set seed, although in all the examples I have examined the pollen was morphologically perfect.