104 



MOEPHOLOGY 



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 

 152. The thorns are in the axils they might be petioles ; sometimes 

 of leaves. 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 mam branch into longer and may bear leaves. 



153. Two or more bucUi 

 are borne in the axils. 



154. Some of the buds pro- 

 duce leafy branches. 



