104 



MORPHOLOGY 



152. The tliorus are ia the axils 

 of leaves. 





it stands for. For example, the foliage in Fig. 151 

 represents green expanded petioles. These leaf -like mem- 

 bers bear buds (which produce 

 branches) in their axils, and they 

 have the arrangement or phyllo- 

 taxy of leaves ; therefore they are 

 considered to be true leaf parts. 

 But they stand edgewise as if 

 they might be petioles ; sometimes 

 they bear leaf -blades; other aca- 

 cias have compound expanded leaves; 

 there are intermediate forms or grada- 

 tions between different acacias; young 

 seedlings sometimes show intermediate 

 forms. From all the evidence, it is now 

 understood that the foliage of the simple- 

 leaf acacias represents leaf -like petioles. 

 Such petioles are known as phyllodia 

 (singular, phyllodium). 



215. Thorns 

 and strong spines are usually 

 branches. The spines of hawthorns 

 or thorn-apples are examples: they 

 are borne in the axils of leaves as 

 branches are (Fig. 152) ; hawthorns 

 usually bear two or more buds in each 

 axil (Fig. 153), and one or two of 

 these buds often grow 

 the following year into 

 normal leafy branches (Fig. 154) ; sometimes 

 the thorn itself bears leaves (Fig. 155). 

 The thorns of wilding pears, apples, and 

 plums are short, hardened branches. In 

 well -cultivated trees there is sufficient vigor 



. . * 155. The thorn 



to push the main branch into longer and may bear leaves. 



153. Two or more bud;^ 

 are borne in the axils. 



154. Some of the buds pro- 

 duce leafy branches. 



