“BREAKING” IN TULIPS. II

SUMMARY The results of the second series of bulb manipulation experiments have confirmed previous results as to the infectious nature of the agent or virus which brings about “breaking” in tulips. “Breaking” can be transmitted by grafting and plugging bulbs with tissue from “broken” bulbs, but injections with filtered sap expressed from “broken” bulbs have given negative results. All attempts to induce parrotting by grafting have been unsuccessful. There appears to be no correlation between the type of “break” of the transmitter and the type of “break” induced. Transmitters vary in potency on different hosts, and different hosts vary in degree of susceptibility towards the same transmitter. Tulipa species have been observed to “break” naturally under garden conditions, and “breaking” has also been induced in the same by grafting with “broken” garden varieties. The bi‐colour variety Keizerskroon has been proved not to be an infectious “break,” but a true bi‐colour; “breaking,” however, can be induced in the red areas of the perianth by grafting with other “broken” varieties. The effect of the virus on the colour plastids and the distribution of the anthocyanin sap pigment is discussed. It is suggested that a knowledge of the translocation of the virus in the bulb is of practical importance to bulb growers. The experiments indicate the importance of aphis control by means of spraying in the growing season and the advantage to be gained by lifting and storage under aphis‐free conditions in the autumn. In conclusion, my thanks are due to Sir D. Hall for information with respect to the initial “breaking” of Zomerschoon and the “breaks” in Tulipa species, and to the laboratory assistant E. F. Emarton for taking the photographs for the plates and for his valuable help in the manipulation of the large number of bulbs treated.