26 



ARRANGEMENT OF LEAVES. 



and more or less appressed to the shoot or concreseent with it. But in 



species in which the branchlets are sub-terete or rounded as in Li'Iidi-ofm.* 



tetragona and in some belonging to the Australian genera Callitris and 



Aetinostrobus the leaves are uniform in size and shape. 



The arrangement of the leaves of the adult foliage in regard to their 



insertion on the principal and lateral axes is either spiral, decussate, 



or whorled.* The spiral arrangement is usually very clearly marked, 



and is by far the most predominant one; it occurs throughout the 



Fig. 11. Sterile branchlet of Abies grandma with leaves spreading in one plane. 



Abietinere (the close-set leaves on the short spurs or arrested 

 branchlets in Cedrus, Larix and Laricopsis are apparent exceptions 

 only), also throughout the Araucarinect, the greater part of the 

 Taxodineie, and the Taxacea?. This spiral arrangement of the leaves is 



* There is no essential distinction between decussate and whorled (verticillate). The 

 difference consists only in the number of leaves completing the circle decussate two, 

 whorled more than two. ami in the relative position of tin- Iwivi-s of one circle to those of 

 the next above or below. 



