142 THE STUDY OF PLANT COMMUNITIES • Chapter VI 



Fig. 73. An Abelia hedge in late fall that (left) ceased growth and hard- 

 ened normally everywhere except section under boulevard light. Here, be- 

 cause of the extended photoperiod, the plants continued to grow and put out 

 new shoots, which were killed by the first heavy frost (right).— From 

 Kramer. 1 * 1 



flowering structures. The differences in photoperiodic response 

 between varieties may be the sole reason for success or failure of 

 a crop at a particular latitude and is an excellent reason for know- 

 ing one's seed stock and its potentialities. Flowering shrubs and 

 herbs, too, if grown beyond their normal latitudinal range, may be 

 pampered and kept alive but often fail to flower because the length 

 of day is unsuitable, or may invariably flower too earlv in the 

 spring or too late in the fall. 



The cessation of growth and subsequent "hardening" of ever- 

 green woody plants are initiated in response to length of day. If 

 plants are put out within range of street lamps, some winter-killing 

 mav be anticipated. Street trees of several species retain their leaves 

 on the side illuminated by street lamps long after dormancy and 

 complete leaf fall on the opposite side, which does not have sup- 

 plemental light. 171 On the Duke University Campus, lamp posts 

 are regularly spaced in a long Abelia hedge, and every winter frost 

 injury results within a certain distance of each lamp because the 

 plants here do not go into dormancy. 147 



