

PLANT MORPHOGENESIS FOR SCIENTIFIC MANAGEMENT OF RANGE RESOURCES 



57 



Table 6. — Leaf lamina length (mm.) of three 

 grass species grown at three day lengths (17) 





Length 



of leaf 



lamina at 







day length 



of— 





Species 



8hr. 





16 hr. 





24 hr 





Mm. 





Mm. 





Mm. 



Orchardgrass 



205 





453 





493 



Meadow fescue 



318 





452 





520 



Perennial ryegrass 



207 





244 





278 



Mean 



243 





383 





430 



diverted to tiller development leading ultimately 

 to flowering. Seasonal variations in dry matter 

 yields coincide with tiller development. This pho- 

 tomorphogenic response, more than any other, 

 may account for the seasonal variations in yield 

 noted for many perennial herbage species, par- 

 ticularly cool -season grasses. 



Floral Development 



Recently, attention has been directed toward 

 the significance of floral development and the 

 associated increase in crop growth rate during 

 this stage of development as well as the lower 

 growth rates during the post-flowering period 

 (6). This is particularly evident for seasonal 

 yields of grass species, and research programs 

 have been developed to alter these growth pat- 

 terns (12). If floral development does indeed 

 stimulate dry matter accumulation, understand- 

 ing the role of environmental factors in floral 

 development takes on added significance in herb- 

 age production. 



Evans (8) and coworkers reported a compre- 

 hensive series of experiments on the flowering 

 physiology of Lolium temulentum L. Their con- 

 clusions likely apply to other long day plants, 

 particularly herbage grass species. Two aspects 

 of floral development that need further elabora- 

 tion pertain to the role of low temperature ex- 

 posure and whether a juvenile stage of develop- 

 ment exists in some herbage species. Bean (1) 

 concludes that both tall and meadow fescue have 

 a juvenile stage during which plants show a re- 

 duced response to inductive conditions. It is more 

 difficult to document such a stage of development 



in herbaceous species compared to deciduous spe- 

 cies. At present, the existence of a juvenile stage 

 remains an open question. It would be important 

 to understand what ph}'siological or environmen- 

 tal conditions are involved in the transition from 

 a juvenile stage to a floral stage if one exists. 



The role of low temperature in floral develop- 

 ment has been associated with vernalization. 

 Floral development of those species that have 

 evolved ecotypes adapted to regions of subfreez- 

 ing winter conditions appears to involve a low 

 temperature requirement. An example of such 

 natural selection can be found in red clover. Red 

 clover has been described as a long-day plant but 

 within some cultivars a segment of the population 

 develops flowers very slowly or remains vegeta- 

 tive under conditions otherwise conducive to 

 flowering. 



Floral stem development of a Finnish variety 

 'Tammisto' was considerably later than that of 

 Penhscott. a cultivar adapted to more temper- 

 ate conditions (3) . Plants grown under 16- or 20- 

 hour photoperiods developed floral stems at essen- 

 tially the same time. The cumulative percentage 

 of floral plants of Pennscott went from to 100 

 within a 4- week time span following the low tem- 

 perature exposure compared to a 7-week time 

 span for plants not exposed to low temperatures. 

 Likewise, the cumulative percentage of floral 

 plants of Tammisto went from to 100 within a 

 6-week period following low temperature ex- 

 posure compared with a 9- week period for plants 

 not exposed to Ioav temperatures. 



An environmental regime that provided short 

 photoperiods rather than long photoperiods 

 during seedling development, followed by low 

 temperature exposure, resulted in the most rapid 

 floral development of the Tammisto plants. 

 Apparently floral development of the Tammisto 

 plants was adversely affected by exposure to long 

 photoperiods prior to low temperature exposure. 

 This effect was not noted for the Pennscott plants 

 (fig. 8). 



The environmental regime providing the most 

 rapid rate of floral stem development was a 

 2-week period at 30° and 12-hour photoperiod 

 during seedling development, followed by 2 weeks 

 at 2° and 10-hour photoperiods, and then 30° 

 and 20-hour photoperiods during the floral de- 

 velopment period. Under these conditions, only 



