56 



MISCELLANEOUS PUBLICATION 1271, U.S. DEPARTMENT OF AGRICULTURE 



Table 5. — Number of tillers per plant of three 

 grasses grown at three day lengths (17) 





Number of tillers 

 length of — 



at 



day 



Species 



8hr. 



16 hr. 





24 hr. 



Orchardgrass 

 Meadow fescue 

 Perennial ryegrass 

 Mean 



10.8 



9.6 



15.2 



11.9 



4.5 



7.4 



10.7 



7.5 





3.8 

 5.8 

 9.9 

 6.5 



compounds accumulated and resulted in greater 

 tillering capacity and a lower top/root ratio. 



Although metabolic substrates are necessary 

 for tiller development, as for any growth process, 

 tillering is obviously a complex plant response 

 reflecting much more than simply environmental 

 control of substrate levels. More likely tillering 

 of perennial herbage species is under control of 



endogenous growth substances that in turn are 

 regulated by the prevailing environment. 



In contrast to tiller response, rate of leaf ex- 

 pansion was shown to be related in a positive 

 manner to photoperiod. Ryle {17) found that leaf 

 length of three grass species was markedly af- 

 fected by photoperiodic conditions (table 6). The 

 rate of leaf appearance (time interval between 

 appearance of successive leaves) in these same 

 species was somewhat higher at short photo- 

 periods (8 hours) than long photoperiods (16 

 or 24 hours). Thus, development of leaf tissue 

 (cell expansion) in perennial cool-season grasses 

 appears to be favored by long day lengths while 

 development of new leaves or tillers is favored 

 by short photoperiods. 



Such plant response coincides with the charac- 

 teristic growth and development of long day 

 plants. Development of regenerative tissue (till- 

 ers) occurs under short day conditions. When 

 the environmental conditions provide long day 

 lengths most of the photosynthetic energy is 



TEMPERATURE 



10 



-• Reed canarygrass 

 -A Climax timothy 



/ 21- 15.5 C 



_L 



± 



_L 



J_ 



LIGHT INTENSITY 



Reed canarygrass 



-A Climax timothy 



40% 



-L 



J_ 



X 



J. 



10 15 20 25 30 

 DAYS 



10 15 20 25 30 

 DAYS 



Fiqube 7. — Tiller numbers in timothy and reed canarygrass plants grown under different light intensities (100 per- 

 cent equals 73 or 80 milliwatts cm.- 2 min. - 1 ) and temperatures (11) 



