7. These daily treatments should be continued until the plants on 8- to 10- 
hour day (those of lot A) take on the aspects of dormancy and there is a 
marked difference in the size of plants of lots A and B. This should 
require at least 30 days. 
q Observations: 
Record date treatments began, length of the light and dark periods, and 
also record the number of short days required to induce dormancy or to 
stop growth of the main axis. Measure at daily intervals and plot the length 
‘, of the main axis of plants from both lots against time in days. 
Supplementary Reading: 
Borthwick, H. A. Light effects on tree growth and seed germination, Ohio 
Jjouns Sci. 57: S57-364;, 1957. 
> Downs, R. J., and Borthwick, H. A. Effects of photoperiod on growth of 
trees. Bot. Gaz. 117: 310-326. 1956. 
Thimann, K. V. The physiology of foresttrees. Pp. 529-583. Ronald Press, 
New York, 1958. 
Wareing, P. F. Photoperiodism in woody plants. Ann, Rev. Plant Physiol. 
1: 191-214: 1956. 
> DEMONSTRATION D-4: Photoperiodic control of bulb formation of onions, 
Materials: 
1. Onion seeds, Plants of southern varieties White Bermuda, Crystal Wax, 
Eclipse, Excel, and Granex hybrid will bulb on 12-hour days. Plants of 
northern varieties Australian Brown, Sweet Spanish, Elite hybrid, and 
Yellow Globe (Early Yellow Globe, Yellow Globe Danvers, Downing 
Yellow, and Globe) will bulb on 15-hour days. 
Sterilized soil. 
Four wooden boxes 8 to 10 inches wide, 10 inches deep, and 12 inches 
long with drainage holes. 
, 4, A light-equipped chamber, 
5. A dark chamber. 
Wh 
Procedure: 
— 
Fill boxes with sterilized soil and level the soil surface. 
1 2. Make two shallow furrows lengthwise of the box 1/4-inch deep and 4 
inches apart. 
3. Plant the seeds thinly in the furrows, cover the seeds with soil, and 
water carefully. Label each box with the name of the variety, the date of 
planting, and the daylength treatment. 
4. When seedlings are well established, thin the plants to 2 inches apart 
} in the row. 
53 ee the seeds and grow the plants at room temperature (70° to 
80> Eye 
25 
