108 



MORPHOLOGY 



164. The thorns are in the axils 

 of leaves. 



leaf -like members have buds (which produce branches) in their 

 axils, and they have the arrangement or phyllotaxy of leaves; 



therefore they are considered to be 

 true leaf parts. But they stand 

 edgewise as if they might be pet- 

 ioles; sometimes they bear leaf- 

 blades; other acacias have com- 

 pound expanded leaves; there are 

 intermediate forms or gradations 

 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 (sin- 

 gular, phyllodium). 



227! Thorns and strong spines are usu- 

 ally branches. The spines of hawthorns 

 or thorn-apples are examples: they are 

 borne in the axils 



of leaves as branches are (Fig. 164); 

 hawthorns usually bear two or more 

 buds in each axil (Fig. 165), and one 

 or two of these buds often grow the 

 following year into normal leafy 

 branches (Fig. 166); sometimes the 

 thorn itself bears leaves. (Fig. 167.) 

 The thorns of wilding 

 pears, apples and plums 



are short, hardened branches. In well-culti- 

 vated trees there is sufficient vigor to push the 

 main branch into longer and softer growth, so 

 that the side buds do not have a chance to 

 start. The thorns of osage-orange and honey- 

 locust are also branches. Those of the honey- may bear 



165. Two or more buds 

 axe borne in the axils. 



166. Some of the buds pro- 

 duce leafy branches. 



