Germination and Early Growth of Cornus florida, Sambucus canadensis, and Berberis thunbergii

Abstract

1. Seeds of Cornus florida are dormant when the fruit is mature. This dormancy, which is caused by embryo and endosperm characters, cannot be broken by treatments with acids, ether, or ethylene. 2. A period of 100-130 days at 0⚬, 5⚬, or 10⚬ C. is most effective for after-ripening, which may be defined as that change in the endosperm and embryo of the seed in consequence of which the seed is able to germinate at ordinary temperatures (15⚬-27⚬). 3. The changes apparent during after-ripening are increase in starch, sugar, and amino acids, with little or no change in fats, acidity, or phosphatides. 4. Germination consists of a rather sudden swelling of the embryo and endosperm, sufficient to break the stony coat followed by the elongation of the hypocotyl. The cotyledons remain within the endosperm, acting as haustoria (43) until all the food reserves are exhausted, after which they function as leaves. 5. After-ripening conditions of cold moist storage may be obtained in mixtures of seeds with sand or peat placed in refrigerators, by burying the containers, or by planting the seeds in beds mulched during the winter. 6. Under natural conditions germination occurs in the spring among those seeds which have lain throughout the winter in moist sheltered spots well covered with leaves. 7. Catalase activity parallels after-ripening very closely. It may be considered an indication of the direction of change, whether toward deeper dormancy or toward germination. 8. Catalase activity has also been used to detect dead seeds. 9. Respiration falls early in the period of exposure to low temperatures for after-ripening, and remains low until germination begins. At higher temperatures (above 15⚬) it remained constant and fairly high for the length of time tried (124 days). 10. Seeds of Sambucus canadensis may or may not be dormant when collected. If not dormant they will grow in 14-30 days at a daily temperature alternation of 10⚬ for 17 hours and 27⚬ for 7 hours or at a similar range of alternation. If dormant they require a period of 85-100 days at 0⚬ or 5⚬, after which they will germinate on subjection to the necessary alternation, or at 0⚬-5⚬ if left long enough. 11. Such seeds when once split grow very well at higher constant temperatures. 12. Exposure to higher temperatures under germinative conditions deepens the dormancy in seeds of both Cornus florida and Sambucus canadensis, as indicated by their failure to germinate and their drop in catalase content. Recovery may be brought about in each case by a period of 130-140 days at 5⚬ C. 13. Seeds of Berberis thunbergii resemble those of Sambucus in that they require alternating temperatures for germination. They differ in that they require only a very short cold treatment or none at all for germination. 14. Seeds of either Sambucus or Berberis thunbergii planted out-of-doors in the autumn, protected from freezing, and exposed to the fluctuating temperatures of early spring, reach from 60 to 70 per cent germination. 15. Freezing in no case favors after-ripening, and always kills large numbers of imbibed seeds. 16. Storage in the pulp, especially in a moist condition, leads in all seeds studied to bacterial and other fungal infection, resulting in a high percentage of killing. This is particularly true for Cornus florida.