130 PHOTOCONTROL OF GROWTH 



Table I. Effect of Kind of Supplemental Light on Growth of Loblolly Pine 



Incandescent" Fluorescent" 



lamp, with high red and almost no far-red emittance, leaves the pig- 

 ment system predominantly in the far-red-absorbing form and thereby 

 reduces growth. 



Herbaceous plants, many of which are able to make elongative 

 growth over a wider range of photoperiods than many woody plants, 

 nevertheless react much as woody plants do to the modulation of 

 elongative growth by the pigment system. For example, soybean 

 (Glycine max (L.) Merr. var. Biloxi and var. Agate) and tomato 

 (Lycopersicum escidentum Mill. var. Marglobe) reacted as loblolly 

 pine did, producing longer internodes when the plants entered the dark 

 period with the pigment system predominantly in the red-absorbing 

 form; that is, under incandescent supplemental light (Table II). Thus, 

 the operation of the regulator as a modulating device is readily demon- 

 strated with herbaceous plants as well as with woody ones. However, 



Table IL Effect of Photoperiod Length and Kind of Supplemental Light on 



Growth of Tomato and Soybean 



Plant 



Marglobe tomato 



Nodes 



Stem length, cm 

 Biloxi soybean 



Nodes 



Stem length, cm 

 Agate soybean 



Nodes 



Stem length, cm 



Photoperiod," 12 hr 



Photoperiod," 16 hr 



Licandescent Fluorescent Incandescent Fluorescent 



8 

 29.3 



10 



90.6 



6 



44.8 



8 

 20.2 



10 



72.2 



5 

 22.0 



9 

 31.8 



10 

 100.0 



5 

 61.9 



18.6 



11 

 68.8 



5 

 26.4 



" Eight hours of natural light plus the duration of supplemental light necessary to obtain 

 these photoperiods. 



