. Contributions from the Botanical Laboratory and the Morris Arboretum of the University of Pennsylvania, vol. 14. Botany; Botany. O 20 30 40 50 60 70 Fig. 7. Curves showing comparative effects of exposure to 24° and 36° C. after exposure to various doses of x-rays. delayed as the temperature decreased. Similar experiments were performed by repeating the dose of 2000 r and also using 1500 and 800 r, in each case exposing part of the irradiated group to 24° and part to 36° C. with their respective controls at each temperature. Figure 5 shows that after both the 1500 and 2000 r treatments, the r
. Contributions from the Botanical Laboratory and the Morris Arboretum of the University of Pennsylvania, vol. 14. Botany; Botany. O 20 30 40 50 60 70 Fig. 7. Curves showing comparative effects of exposure to 24° and 36° C. after exposure to various doses of x-rays. delayed as the temperature decreased. Similar experiments were performed by repeating the dose of 2000 r and also using 1500 and 800 r, in each case exposing part of the irradiated group to 24° and part to 36° C. with their respective controls at each temperature. Figure 5 shows that after both the 1500 and 2000 r treatments, the roots grown at 24° lived longer than those in the group at 36° C. Growth after 1500 r extends over a longer period of time at the lower temperature, and, also, the roots reach a considerably greater length before death when grown at 24° than at 36° C. Figure 6 shows that when the dose is lowered to 800 r, the irradiated groups grown at 120 100 90 u ao UJ J 2 60 Z 50 X O 40 z u -" 30 20 10 /. / 4 / 24" 2000 R i / T 10 ao 30 40 50 TIME 60 70 10 IN HOURS 20 30 40 50 Fia. 8. Growth curves showing effect of temperature on length of latent period after an x-ray dose of 2000 r. «Va RUSSELL: EFFECTS OF X-RAYS ON ZEA MAYS 127 the two temperatures grow roughly parallel to each other, the 36° group growing the faster just as the 36° controls grow faster than the 24° controls. In figure 7 the curves of the growth following the three doses have been rear- ranged to show more graphically the effect of the two temperatures on each. The curves in figures 4, 5, 6, and 8 show that with all the doses used, the latent period was longer at the lower temperature. As the dose increases, the difference between the temperature effects is increased. Discussion The coleoptile was the only part of the corn seedling which failed to show any effects of irradiation. Cattell (3) reported it to be the least sensitive part of wheat, as after a dose of 1200 r the coleoptiles showed a reducti
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