156 



MISCELLANEOUS PUBLICATION 1271, U.S. DEPARTMENT OF AGRICULTURE 



Profile depth: 82.5 - 90 cm 



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ND J FMAMJ JAS ON 

 Month 



Figure 5. — Variations in soil moisture in phenology plot 

 during 1969-70. Upper dashed line in each graph repre- 

 sents 0.1 atmosphere percentage, lower dashed line 15 

 atmosphere percentage. 



are seldom completely buried and germination 

 usually occurs on the soil surface. Seeds will not 

 germinate under conditions of high moisture 

 stress. This could be an adaptive characteristic 

 of species subjected to severe drought conditions 

 {5,26, 47). 



The effect of fruit weathering on germination 

 was followed for only 14 months but indications 

 are that germination improves exponentially 

 (fig. 6). A tentative prediction is that a germi- 

 nation of 40 to 50 percent could be attained about 

 3 years after fruit matures. Low initial germina- 

 tion is attributed to an impervious, woody peri- 

 carp. There is no evidence of toxic inhibitors con- 

 trolling seed germination of this arid shrub (18, 



Maximum germination at constant tempera- 

 tures occurs between 15° and 25°C. Koller (19) 

 suggested that temperature controls germination 

 when rainfall is nonseasonal. Further, optimal 

 conditions are more likely to be those inducing 

 the most rapid rather than the highest percentage 

 germination. Rate of germination is defined as 



Table 2. — Field germination {thousands /ha.) of 

 Eremophila gilesii fruits over 14- days follow- 

 ing 60 mm rain in March and September 1970 



Period 



Ground fruit 



Number Percent 



germinated germination 



March 

 September 



4285±475 

 4285±475 



74±13 



278±22 



1.7 



6.5 



the reciprocal of the number of days to reach 50 

 percent of final germination {27). For E. gilesii, 

 the maximum rate (derived from fig. 7) occurs 

 between 25° and 35° C. 



While the lower range of temperatures tested 

 may be suboptimal for germination it can be in- 

 ferred from figure 7 that temperatures higher 

 than 40° C. could be lethal. Turner (37) showed 

 a relationship between maximum screen and soil 

 surface temperatures in Central Australia. The 

 community and soil of his study were similar to 

 those in which E. gilesii occurs. At screen maxi- 

 mum temperatures of 30° and 40° soil tempera- 

 tures were approximately 50° and 70°, respective- 

 ly. A similar relationship can be expected in the 

 present study area. 



Although Turner's relationship applies only to 

 cloudless periods at least one week after last rain, 

 the effect is of such magnitude that temperatures 

 inhibitory to germination can be anticipated 





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Months weathered 





Figure 0. — Effect of weathering on fruit weight (x) and 

 germination (.) in Eremophila gilesii. Germination 

 data presented ± standard error. Fruit weight is mean 

 of 1,000 fruits. Both curves fitted by eye. 



