PLANT MORPHOGENESIS FOR SCIENTIFIC MANAGEMENT OF RANGE RESOURCES 



103 



species, which are significant to livestock produc- 

 tion in temperate and tropical Australia and for 

 which data are available. 



Hordeum leporinum (barley grass) is a nat- 

 uralized Mediterranean annual grass. Barley 

 grass, commonly associated with burr medics, in- 

 vades pastures of Wimmera ryegrass — barrel 

 medic and Wimmera ryegrass — subterranean 

 clover. In recent years, it has also invaded heav- 

 ily fertilized and heavily grazed perennial 

 grass — subterranean clover pastures. Barley grass 

 provides early winter feed for livestock (4-1), but 

 its sharp pointed floral structures are a cause of 

 vegetable fault in wool and are injurious to ani- 

 mals, particularly to lambs in the spring (32). 

 Because of these harmful attributes, attempts 

 have been made to eradicate it from sown pas- 

 tures, and studies have been made of its com- 

 petitive interrelationships with Wimmera rye- 

 grass, a preferred species. 



In a grazing experiment of Robards and Leigh 

 (32) at Deniliquin, New South Wales, Burt (9) 

 determined the height of shoot apices in barley 

 grass at different stages of development. These 

 relationships are shown in figure 3. Using other 

 data from Burt (9) an approximate time scale 

 has been superimposed on the horizontal axis. 



Leaf primordia Formation of 

 only side spikelets 



Maximum recorded ht. at which 



Flower head 

 emerging 



growing points were removed 



Treatment 

 • 1 

 o 2 



Minimum recorded ht. at which 

 growing points were removed 



3 



4 5 6 7 8 



9 



10 



11 



MAY 



JUNE JULY 

 Reproductive stage 



AUG 





SEPT 



Figure 3. — Height of shoot apices in barley grass at dif- 

 ferent stages of development. (From Burt, 9. with su- 

 perimposed time scales.) 



The relationship between height of shoot apices 

 and various stages of development was not af- 

 fected by withholding grazing (Treatment 1), 

 grazing in May and June (Treatment 2), and 

 grazing monthly (Treatment 3). 



When shoot apices were about 2 cm. above the 

 ground they became accessible to sheep. Un- 

 grazed plants attained this height about the end 

 of July and those grazed monthly, about mid- 

 August. Removal of shoot apices by grazing in 

 August and September stimulated production of 

 axillary tillers from basal buds and increased 

 the number of flower heads in comparison with 

 ungrazed plants. In September, tiller numbers 

 on ungrazed plants were 1.36 per plant compared 

 with 3.74 per plant on monthly grazed plants. 



Lolium rigidum (Wimmera ryegrass) is a sown 

 annual grass. Cooper and Saeed (13) made com- 

 parative studies of growth and development of 

 Wimmera ryegrass and perennial species of Lo- 

 lium. They found that, under continuous light, 

 the annual species produced 8-12 leaves before 

 floral initiation. Under the same conditions, Lo- 

 lium perenne L. (S24) produced more than 20 

 leaves before becoming reproductive. When de- 

 foliated during stem elongation, Wimmera rye- 

 grass — like barley grass — produced secondary til- 

 lers which elongated with fewer leaves and pro- 

 duced flower heads more rapidly than the pri- 

 mary tillers. Because the primary tiller appar- 

 ently influences the "ripeness to flower" of its 

 axillary buds, Cooper and Saeed argue that indi- 

 vidual tillers of the grass plant a?e not inde- 

 pendent. 



Sown in Melbourne (lat. 38° S.), Wimmera 

 ryegrass initiated flowers in late June and most 

 shoot apices were 2 cm. above the ground by 

 mid- August (5). This ryegrass is slightly later 

 than barley grass but its seasonal growth pattern 

 is similar. 



Silsbury (4-0) found that tillering in Wimmera 

 ryegrass increased slowly before stem elongation 

 in June and July. It increased rapidly during 

 stem elongation until September when the rate 

 steadied, and then declined to November, the 

 period of flowering and seed formation at lat. 

 35° S. Cessation of tillering from September on- 

 wards appeared to be associated with onset of 

 heading, decrease in soil nitrogen, increase in 



