PLANT MORPHOGENESIS FOR SCIENTIFIC MANAGEMENT OF RANGE RESOURCES 



53 



200 



• Bromegrass 

 X Orchardgrass 

 O Timothy 



15 



20 25 30 



TEMPERATURES, C 



35 



Figure 5. — Dry matter accumulation in grass seedlings 

 grown for 3 weeks at temperatures ranging from 15° 

 to 35° C. 



Garza and others (9) found that growth of al- 

 falfa seedlings, as measured by dry matter ac- 

 cumulation, was considerably higher at 30° C. and 

 a light intensity of 43,000 lux than at the same 

 temperature but at a light intensity of 11,000 

 lux (fig. 6). A temperature of 30° during the 

 light and 15° during the dark period resulted in 

 higher growth rates than constant temperatures 



of 15° or 30°. This response was noted at both 

 high and low light intensity. They concluded 

 that temperature response was affected by light 

 intensity and further that plant response changed 

 with advancing age. However, low light inten- 

 sity combined with high temperature was detri- 

 mental to growth of alfalfa at all stages of de- 

 velopment. 



Vegetative Development 



As a seedling develops, buds near the soil sur- 

 face are activated, leading to tiller formation and 

 growth. Physiological and environmental re- 

 sponses of plants that have reached a stage of 

 development where tiller production is relatively 

 stable are different from responses of seedling 

 plants. Tiller formation and development are of 

 paramount importance in herbage production; 

 consequently, extensive research has been con- 

 ducted on this aspect of morphological develop- 

 ment. 



Tillers develop from activation of axillary 

 buds or initiation of adventitious buds. There- 

 fore, research has been primarily concerned with 

 what physiological, environmental, or manage- 

 ment factors are involved in the control of these 

 buds and, more specifically, control of tiller de- 

 velopment. This is particularly true of research 

 on tiller development in perennial grasses where 

 tillers arise from axillary buds. However, in the 

 case of some legumes, tillers develop from ad- 

 ventitious buds arising from crown or root tissue. 



Emphasis on developing alfalfa varieties with 

 a creeping-rooted character has pointed to the 

 need for a more complete understanding of ad- 

 ventitious bud formation in this species. Carlson 



Table 2. — Ratios of aerial/root tissue dry weights of legume 

 and grass seedlings grown at five temperatures for 3 weeks 



Species 



15° C. 



20° C. 



25° C. 



30° C. 



35° C. 



Alfalfa 



2.72 



3.81 



3.70 



4.33 



4.47 



Red clover 



2.53 



3.03 



3.00 



4.20 



•7.03 



Birdsfoot trefoil 



1.74 



3.73 



5.00 



5.08 



4.70 



Ladino clover 



2.26 



3.58 



3.02 



3.80 



4.83 



Bromegrass 



1.33 



1.34 



1.30 



1.98 



'7.30 



Orchardgrass 



1.94 



2.40 



2.67 



3.39 



'6.36 



Timothy 



1.15 



1.80 



2.36 



3.44 



•aoo 



1 Based on limited seedling growth and development. 



