DESCRIPTIVE BOTANY. 



PART I. 



reference to its marginal incisions ; then they should 

 consider the character of the incisions, and the relation 

 they bear to the disposition of the veins. In com- 

 pound leaves, the degree to which the subdivisions 

 of the petiole take place must be considered, and the 

 analogy noted, which exists between the disposition of 

 the partial petioles and the venation of simple leaves. 

 Thus the student will soon learn to fix in his memory 

 the numerous modifications of form which leaves pre- 

 sent. 



(75.) Phyllodium. There are some plants, as many 

 of the acacias of New Holland, in which the limb of 

 the leaf is not developed, but the petioles themselves are 

 laterally compressed, and so much flattened out as to 

 assume the appearance of a limb ; except that they affect 

 a vertical position instead of a horizontal one, and that 

 there is no apparent difference between their two sur- 

 faces in colour, or other characters. In young plants 



of this description, however, and occasionally also in old 

 ones which have been freely pruned, we may observe all 

 the intermediate states or varieties between a doubly 



