Oct. I, 1919-Mar. 15, 1920 



Illustrations xv 



Germination of Barley Pollen 



Page 



Plate 60. A. — Normal pollen. B. — Bulging of the intine through imbibition. 

 C. — The effect of free water when the intine is not ruptured. D. — Pollen 

 germinating on a stigma hair; the pollen grain loosened so as to show the 

 tube. E. — Germinating pollen. F, G. — Pollen tube 536 



Plate 61. A. — Normal pollen grains. B. — Same pollen grains after an ex- 

 posure of two minutes to dry air 536 



Basal Glumerot of Wheat 



Plate 62. Basal glumerot of wheat: A. — Heads showing diseased glumes. 

 B. — Glumes diseased at base. C. — Grains black and full of bacteria at 

 base. D. — Young wheat leaves five days after inoculation with Bacterhim 

 atrofaciens. E- — Glumes inoculated with strain 478. F. — Glumes inocu- 

 lated with strain 399. a, Inner face 552 



Plate 63. Various types of colonies of Bacterium atrofaciens: A. — Moder- 

 ately crowded colonies on agar plate, 3 days old. B. — Well-isolated colo- 

 nies on agar plate, 2 days old. C. — Single colony on agar plate, 20 days 

 old. D. — Well-isolated colonies on agar plate, 3 days old. E. — Crowded 

 colonies on agar plate, 2 days old. A and E represent the ordinary type 

 of young colony. F. — Flagella (Van Ermengem's stain) 552 



Effect of the Relative I,encth of Day and Night and Other Factors 

 OF THE Environment on Growth and Reproduction in Plants 



Plate 64. A. — Small dark chamber used in the 19 18 experiments. B. — 



Larger dark house used in the 1919 tests 606 



Plate 65. A. — Peking soybeans exposed to the light for 7 hours daily. B. — 

 Control planting of Peking soybeans exposed to the light for the whole 

 day — that is, kept out of doors day and night 606 



Plate 66. A. — Peking soybeans exposed to the light for 7X hours dail)', 

 beginning with the blossoming period. B. — Control planting of Peking 

 soybeans kept out of doors throughout the test 606 



Plate 67. A. — Biloxi soybeans exposed to the light for 7 hours daily. B. — 



Control planting of Biloxi soybeans kept out of doors during the test 606 



Plate 68. Biloxi soybeans: A. — Plants in box on left exposed to the light for 

 5 hours daily. B. — Plants in box on left exposed to light daily for 7 hours; 

 those on right exposed 12 hours daily 606 



Plate 69. A. — Biloxi soybeans. Plants in box on right exposed to light from 

 daylight to 10 a. m. and from 2 p. m. to dark, a total of 9 to 10 horns daily. 

 Plants in box on left exposed to light from 6 a. m. to6p. m.,or 12 hoiu-s daily. 

 B. — Radish plant in which the seed stalk was transformed into a vegeta- 

 tive shoot through the influence of the decreasing length of day. 



Pirate 70. A. — Maryland Mammoth tobacco in S-inch pots exposed to light 

 from 9 a. m. to 4 p. m. daily. B. — Control series of Maryland Mammoth 

 plants kept out of doors 606 



Plate 71. A. — Maryland Mammoth tobacco in 12-quart buckets exposed to 

 light from 6 a. m. to 6 p. m., or 12 hoxu^ daily. B. — Maryland Mammoth 

 tobacco in 12-quart buckets exposed to light from 9 a. m. to 4 p. m., or 7 

 hours daily 606 



Plate 72. A. — Control series of Mar>'land Mammoth tobacco in 12-quart 

 buckets left out of doors during the experiment. B. — Asf^r hnariifolius 

 L. Plants in box on left exposed to light from 9 a. m. to 4 p. m. daily. 

 Plants in box on right left out of doors during the test 606 



