36 PHARMACEUTICAL BOTANY 



Like roots, they differ greatly as to duration in different latitudes. 

 Evergreen trees are most common in the tropics, and it is probable 

 that many of our deciduous trees have become such by adaptation to 

 the colder climate. 



Leaf Insertion. — The point of attachment of the leaf to the stem is 

 called the insertion. A leaf is: 



Radical, when inserted upon an underground stem. 



Cauline, when upon an aerial stem. 



Ramal, when attached directly to a branch. 



When the base of a sessile leaf is extended completely around the 

 stem it is perfoliate, the stem appearing to pass through the blade. 

 Ex. : Urularia perfoliata or Mealy Bellwort. 



When a sessile leaf surrounds the stem more or less at the base, it is 

 called CLASPING. Ex.: Poppy (Papaver somniferum). 



When the bases of two opposite leaves are so united as to form 

 one piece, they are called connate-perfoliate, as Eupatorium or 

 Boneset. 



Leaves are called equitant when they are all radical and succes- 

 sively folded on each other, as the Iris. 



Phyllotaxy. — Phyllotaxy is the study of leaf arrangement upon the 

 stem or branch, and this may be either alternate, opposite, whorled, or 

 verticillate, or fascicled. It is a general law in the arrangement of 

 leaves and of all other plant appendages that they are spirally disposed, 

 or on a line which winds around the axis like the thread of a screw. The 

 spiral line is formed by the union of two motions, the circular and the 

 longitudinal, and its most common modification is the circle. 



In the ALTERNATE arrangement there is but one leaf produced at 

 each node. 



Opposite, when a pair of leaves is developed at each node, on oppo- 

 site sides of the stem. Ex.: Mints, Lilac. 



Whorled or Verticillate, when three or more form a circle about 

 the stem. Ex.: Canada Lily and Culver's root. 



Fascicled or Tufted, when a cluster of leaves is borne from a single 

 node, as in the Larch and Pine. 



The spiral arrangement is said to be two-ranked when the third leaf 

 is over the first, as in all Grasses; three-ranked, when the fourth is over 

 the first. Ex.: Sedges. The five-ranked arrangement is the most 

 common, and in this the sixth leaf is directly over the first two turns 

 being made around the stem to reach it. Ex. : Cherry, Apple, Peach 



