58 Transactions. 



ture of this form, and, later, a comparison with the awl-shaped 

 leaf will leave no doubt as to what changes have taken place. 



The epidermis at this early stage is very much thickened, 

 as is also the cuticle. 



The stomata are confined to four regions, which are the 

 corners of a rectangle, with the bundle for the centre. 



The hypoderm is well developed, but does not form a con- 

 tinuous band. 



The chlorophyll parenchyma at the margins and along the 

 sides consists of large ordinary parenchyma cells. In the middle 

 of the leaf, radiating out from the bundle to the sides and mar- 

 gins, are long, narrow, and in some cases curved, elements. 

 These would evidently serve for conduction of water, but it is 

 doubtful, however, whether they owe their modification primarily 

 for this purpose. The smallness of the leaf makes this modi- 

 fication unnecessary, and it is more probable that they originated 

 in quite a different manner, as will be seen by a comparison 

 with the next section. 



The vascular bundle, as seen in the diagram, is slightly nearer 

 one end than the other. It contains a resin-canal opposite the 

 nearer margin, which is strengthened by a row of sclerenchyma. 

 The px is turned towards the further margin, and between the 

 px and the resin-canal are the very scanty elements of phloem 

 and wood. There are two or three elements of transfusion 

 tracheids starting from the px and running out to the sides, 

 and an occasional element is also found outside the px corre- 

 sponding to centripetal xylem. 



Awl-shaped Leaf. 



The cuticle and epidermis are better developed in the awl- 

 shaped leaf. This may be expected, for the two kinds of leaves 

 are exposed to the same conditions, and the smaller form has so 

 little tissue that it would wither very easily unless it had great 

 protection against excessive transpiration. This view is not 

 altered by the fact that transpiration is lessened by decrease 

 of surface. 



The stomata here, as in the preceding leaf, occur in four 

 regions, but two regions are here about opposite the vascular 

 bundle, the other two being on the sides representing the upper 

 surface of the leaf. 



The hypoderma is well developed at the two most prominent 

 margins, but is broken by the stomata along the rest of the 

 surface. 



The arrangement of the chlorophyll parenchyma differs in 

 one important respect from that of the preceding leaf : there 

 are no elongated elements on the morphologically lower surface 



