PLANT MORPHOGENESIS FOR SCIENTIFIC MANAGEMENT OF RANGE RESOURCES 



115 



with a rapid growth rate during the early stages. 

 Variability in speed of germination exists among 

 widely differing geographic collections of Taeni- 

 atherum as / pei 1 wm seeds in the United States (41)- 

 Collections from areas with a higher degree of 

 uncertainty in the first rainfall appeared to germ- 

 inate at a more rapid pace than did seeds from 

 more mesic sites in the coastal region of Oregon. 



Whalley and others (58) showed that increas- 

 ing soil fertility increased seed size and rate of 

 germination. Soil moisture stress during seed pro- 

 duction reduced the number of seeds, but seed 

 quality apparently was not materially affected. 

 Inasmuch as seed size apparently is a critical 

 factor in promoting greater seedling vigor (57), 

 any management practice which would result in 

 improving seed size should have a corresponding- 

 ly beneficial affect on seedling vigor and estab- 

 lishment. 



Rapid mobilization of food reserves in the seed 

 to soluble forms has been postulated as a possible 

 index to seedling vigor (56). Species known for 

 low seedling vigor apparently were slower in the 



mobilization of food reserves than was a species 

 known for its higher degree of seedling vigor 

 (fig. 1). Seed size in itself does not appear to be 

 a sole criterion of seedling vigor but is meaning- 

 ful only within a species or closely related group. 

 Rapidity of carbohydrate mobilization varies 

 among species. However, one of the most rapid 

 mobilizations reported in the literature is that of 

 Schismus arabicus (Nees.) (57). In this extreme- 

 ly small-seeded annual grass, mobilization of 

 stored carbohydrate was almost complete within a 

 48-hour period. 



Seedcoat hardness or impermeability often re- 

 tards germination. This problem, however, is less 

 common among grasses than among dicotyle- 

 donous species, particularly the annual legumes. 

 The hard seedcoat may have an ecological ad- 

 vantage. Williams (61) demonstrated that hard 

 seeds of Trifolium hirtum All. provided suffi- 

 icient seed for survival of the species, when the 

 seedlings which germinated first were eliminated 

 by drought, following the originally favorable 

 conditions for germination. The remaining hard 



p tuberosa var stenoktera 

 (Tule Springs) 



STARCH 



TOTAL SUSARS 



REDUCING SUSARS 



NON-REOUCINS SUSARS 



SEEDLING LENGTH 



COERULESCENS 



STARCH 



TOTAL SUGARS 



RE0UCIN6 SUSARS 



N0N-RE0UCIN6 SUGARS 



SEEDLING LEN6TH 



■^■tff— ^— ¥— ^ -^- ^*" 



TIME FROM PLACING ON BLOTTERS 

 (DAYS) 



150 i 



Figure 1. — Mobilization of carbohydrate reserves in early seed germination. (Whalley and McKell, (58).) 



