154 



MISCELLANEOUS PUBLICATION 1271, U.S. DEPARTMENT OF AGRICULTURE 





Figure 2. — Fence line contrast between two properties. Note dense Eremophila gilesii at right of fence (stocking 

 rate approximately 1 sheep per 5 ha. since 1965). Little E. gilesii can be seen on left side of fence (stocking 

 rate approximately 1 sheep per 3 ha. since 1956). Tree in background is Acacia aneura. Broad-leaved trees on 

 right are Eucalyptus populnea Hook. Note lack of grass on either property. 



leaves are shed while smaller but still functional 

 leaves remain on the branch apices. Cunningham 

 and Strain (6) found that seasonal variability 

 in leaf numbers enhances the capacity of desert 

 shrubs to maintain a favorable water balance un- 

 der stress conditions and thus remain photosyn- 

 thetically active further into dry periods. It 

 seems that it may be physiologically advantage- 

 ous for plants in arid and semiarid regions to 

 have smaller leaves because of their lower leaf 

 temperatures (11). 



Data from figures 3 and 4 suggest that all 

 phases of reproduction can occur at any time of 

 the year. The number of buds retained in a dor- 

 mant state during drought is proportionately few 

 but permits the plant to rapidly produce some 

 flowers in response to rainfall which otherwise 

 may be insufficient for flowering. However, favor- 

 able conditions for vegetative, bud, and flower 

 development do not necessarily result in produc- 

 tion of fruits. This is particularly noticeable dur- 



ing the summer months. Reasons for this could be 

 excessive heat leading to desiccation of floral 

 parts, inactivation of insect pollinators, or both. 

 Alternatively, the soil profile could be insuffi- 

 ciently moist (fig. 5) to permit complete matura- 

 tion of fruits. 



Fruit production occurs only following rain- 

 fall in excess of 60 mm. This is not to imply 

 that 60 mm. is a minimum for fruit production 

 as other factors including antecedent moisture 

 levels are involved. Zahner (48) concluded from 

 horticultural studies that final size and quality 

 of individual fruits are regulated by the amount 

 of water available during enlargement. The im- 

 plication of this finding for the present study is 

 that where fruit have developed at low soil mois- 

 ture levels their viability is probably impaired. 

 It was observed that fruit produced in the sum- 

 mer months were noticeably smaller than those 

 produced following autumn and early spring 

 rains. 



