'V^ent — 157 — Thermoperiodicity 



The shift in optimal photo- and nyctotemperature according to the hght 

 intensity during the photoperiod, which was found in the tomato experi- 

 ments in the air-conditioned greenhouses is well known in commercial prac- 

 tice, as indicated previously. In future work a further differentiation of the 

 nyctotemperature effect must be made, and a more precise localization of the 

 temperature effect has to be achieved. 



The seeds of many plants germinate well only when they are subjected 

 to a daily fluctuation in temperature (Harrington 1923). This does not 

 seem to be a case of thermoperiodicity in the sense that processes with dif- 

 ferent optimal temperatures have to alternate to cause germination. This is 

 perhaps best demonstrated by the experiments of Morinaga (1926) who 

 found that seeds of Cynodon dactylon require alternation of temperature for 

 best germination, but that scarification for 3-9 minutes with concentrated 

 sulphuric acid made optimal germination possible without alternation of 

 temperature. Toole (1940) found the same effect for Orysopsis. It is also 

 demonstrated by the fact that not the actual temperatures employed, but the 

 alternation of temperatures as such determine germination (Harrington 

 1923). Therefore the seat of response to alternating temperatures seems to 

 be in the seed coat and not in the embryo. The alternating temperatures 

 seem to affect the "encasing structures interfering with oxygen absorption 

 by the embryo and perhaps carbon dioxide elimination from it, resulting in 

 the limitation of the processes dependent upon these" (case 4 of Crocker 

 1916). This conclusion differs from the one reached by Morinaga (1926), 

 who concluded that "alternating temperatures have their effects on the 

 embryos." 



References: — 



Barton, L. V., and Schroeder, E. M., Contr. Boyce Thompson Inst. 12: 277-300, 1942.— 

 Bennett, J. P., Oserkowsky. J., and Jacobson, L., Amer. Jour. Bot. 27: 883-887, 1940. — Ben- 

 nett, J. P., and Skoog, F., Plant Physiol. 13: 219-225, 1938. — Blaauw, A, H., Verh. Kon. Akad. 

 Wetensch. Amsterdam 23, No. 4: 1-66, 1924. — Blaauw, A. H., Verh. Kon. Akad. Wetensch. 

 Amsterdam 29, No. 1: 1-90, 1931. — Blaauw, A. H., Hartsema, A. M., and Huisman, E., Proc. 

 Kon. Akad. Wetensch. Amsterdam 35: 803-812, 1932. — Blaauw, A. H., Luyten, I., and Hartsema, 

 A. M., Verh. Kon. Akad. Wetensch. Amsterdam 26, No. 7: 1-105, 1930. — Bonner, J., Bot. Gaz. 

 104: 475-479, 1943. — Bonner. J., Bot. Gaz. 105: 233-243, 1944. — Chandler, W. H., Kimball, 

 M. H., Philp, G. L., Tufts, W. P., and Weldon, G. P., Bull. Calif. Agric. Expt. Sta. 611: 1-63, 

 1937. — Coster, Ch., Ann. Jard. Bot. Buitenzorg 35: 125-162, 1926. — Crocker, W., Am. Jour. 

 Bot. 3: 99-120, 1916. — Denny, F. E., Contr. Boyce Thompson Inst. 12: 375-386, 1942. — Guthrie, 

 J. D., Contr. Boyce Thompson Inst. 9: 265-272, 1938. — Guthrie, J. D., Contr. Boyce Thompson 

 Inst. 11: 261-270, 1940. — Hamner, K. C, and Bonner, J., Bot. Gaz. 100: 388-431, 1939.— 

 Hartsema, A. M., and Luyten, I., Proc. Kon. Akad. Wetensch. Amsterdam 36: 120-127; 210-216, 

 1933. — Hartsema, A. M., Luyten. I., and Blaauw, A. H., Verh. Kon. Akad. Wetensch. Amster- 

 dam II, 27, No. 1: 1-46, 1930. — Harrington, G. T., J. Agric. Res. 23: 295-332, 1923. — Klebs, 

 G., 1896: Die Bedingungen der Fortpflanzung bei einigen Algen und Pilzen (Jena). Ed. 2, 1928, 

 pp. 543. — Klebs, G., Jahrb. wiss. Bot. 32: 1-70, 1898. — Kuijper, J., Rec. Trav. Bot. Neerl. 30: 

 1-22. 1933. — Lammerts, W. E., Amer. Jour. Bot. 29: 166-171, 1942. — Laurie, A., and Kiplinger, 

 D. C, Commercial Flower Forcing. Ed. 4, Philadelphia, 1944. — Lewis, H., and Went, F. W., 

 Amer. Jour. Bot. 32: 1-12, 1945. — Loo, S. W., Amer. Jour. Bot. 33: 382-9, 1946. — Luyten, I., 

 Versluys, M. C, and Blaauw, A. H., Verh. Kon. Akad. Wetensch. Amsterdam II, 29, No. 5: 1-64, 

 1932. — Michener, H. D., Amer. Jour. Bot. 29: 558-568, 1942. — Morinaga, T., Amer. Jour. 

 Bot. 13: 141-159, 1926. — Roberts, R. H., Science 98: 265, 1943. — Sachs, J., Jahrb. Wiss. Bot. 2 

 (Gesanun. Abh. 1): 49-83, 1860. — Schimper, A. F. W., Pflanzen-Geographie auf physiologischer 

 Grundlage, Jena, 1898. — Slogteren, E. van, Tijdschr. over Plantenz. 42, 1936. — Slogteren, E. 

 VAN, Daffodil Year-book 1935: 48-55. — Toole, V. K., Jour. Amer. Soc. Agron. 32: 33-41, 1940.— 

 Versluys, M., Verh. Kon. Ak. Wetensch. Amsterdam II, 25, No. 4: 1-100, 1927. — Went, F. W., 

 Amer. Jour. Bot. 31: 135-150, 1944. — Went, F. W., Amer. Jour. Bot. 31: 597-618, 1944o. — Went, 

 F. W., Science 101: 97-98, 1945. — Went, F. W., Amer. Jour. Bot. 32: 469-479, 1945a. 



Addilioval References: — Blaauw, A. H., Luyten, I., and Hartsema. A. M., Proc. Kon. 

 Akad. Wetensch. Amsterdam 35: 485-497, 1932. — Dorland, Robert E. and Went, F. W., Amer. 

 Jour. Bot. 34: 393-401, 1947. — Luyten, I., Joustra, G., and Blaauw, A. H., Proc. Kon. Akad. 

 Wetensch. Amsterdam 29: 113-126, 1925. 



