Some Photo‐Dependent Responses in Pisum. I. Physiological Behavior1

Two new (G‐ and G2) and two previously known (K and I) photo‐dependent response types of Pisum were compared in a phytotron after having been distinguished earlier under greenhouse conditions. In the first of two experiments the four response types were exposed to three photoperiods, 9, 12, and 15 hours, at a constant growth temperature of 17 C. Plants of the K‐type exhibited a quantitative increase in nodes and days to flower in response to decreasing length of photoperiod, whereas I‐type plants were day‐neutral or insensitive to length of photoperiod. Flowering in G‐type plants was either completely inhibited or sharply delayed at all three photoperiods. G2‐type plants, like the I‐type, were insensitive to daylength with respect to nodes to flower but, unlike the I‐type, they exhibited a protracted period of apical growth, again at all photoperiods. The behavior of the G‐ and G2‐types at the 15 hour photoperiod was atypical since under long day conditions in the field or greenhouse these types ordinarily do not show a response. The response types were not discriminated under the conditions of a second experiment which included two levels of light intensity and two levels of growth temperature and a long (18‐hour) photoperiod. Growth temperature had no influence on the number of nodes to flower but it had a marked influence on the number of days to flower.