Plant Defences 



85 



how the Port Jacksons get their long narrow leaves and the 

 Mimosas get their thorns. 



When petioles flatten and take the place of the usually 

 expanded portion of the leaves, they are called phyllodes 

 (having the form of leaves). The Mimosa and the Port 

 Jackson look very unlike as trees. But their early history 

 shows that they are really closely related. Their flowers and 

 fruit show the relationship also, so their book name is the 



Fig. 89. — A nosegay from the Karroo. 



same, Acacia. The thorn tree of the Karroo is Acacia 

 horrida ; its Australian cousin is Acacia melanoxylon (black 

 wood). 



Notice the bushes and trees about your district. Are their 

 edges or their flat surfaces turned toward the sun ? The slender 

 green branches of the beef-wood tree {Casuarina) take the 

 place of leaves. This tree also comes from the " land of 

 shadowless forests." 



