PLATE i 
Poinsettia: 
The individuals in center and at right are the same plants that are shown in earlier 
stages in' Plate 19, A. Early in September the plant shown at left in Plate 19, A, was 
transferred to the greenhouse, where it received electric illumination from sunset till 
midnight in addition to the natural daylight. In response to the lengthened daily light 
period, the high-colored bracts soon began to assume a green color, particularly in 
transmitted light. Some of the bracts lost the original red color more or less com¬ 
pletely. Finally, a new shoot appeared at the apex of the flowering stem. In the 
early stages of development this shoot was of the weak, pendent type and the bark of 
the stem was red. Subsequent development of this stem is shown in Plate 19, B. The 
plant at right, maintained under long-day conditions throughout the test, continued 
to develop a vegetative stem. The plant at left received the same treatment as the 
individual in center, except that the electric illumination from sunset till midnight 
was omitted. Nothing remains of the inflorescence except the naked stem. Painted 
from a photograph made January 9. 
