Why do you think the term short day plant is misnomer?

These plants require a relatively short day light period (usually 8-10 hours) and a continu­ous dark period of about 14-16 hours for subsequent flowering (Fig. 18.1A). Some examples of these plants which are also known as long-night-plants are Maryland Mammoth variety of to­bacco (Nicotiana tabacum) Biloxi variety of Soybeans (Glycine max), Cocklebur (Xanthium pennsylvanicum).

i. In short day plants the dark period is critical and must be continuous. If this dark period is interrupted even with a brief exposure of red light (660-665 mµ wavelength), the short day plant will not flower (Fig. 18.1B).

ii. Maximum inhibition of flowering with red light occurs at about the middle of critical dark period.

iii. However, the inhibitory effect of red light can be overcome by a subsequent exposure with far-red light (730-735 mu wavelengths).

iv. Interruption of the light period by dark does not have inhibitory effect on flowering in short day plants (Fig. 18.1 C).

v. Prolongation of the continuous dark period initiates early flowering in short day plants.