Griffin.-— Development of Neiv Zealand Conifer Leaves. 67 



Anatomical Structure. 



The structure of leaves on the young plant corresponds very 

 closely to that of a miro-leaf on a plant of the same size, though 

 the shape in transverse section is more like a totara-leaf. 



The large form of the mature leaf is also very similar, hut 

 has increased enormouslv in size in comparison with the former 

 leaf. 



We still find a total absence of hypoderm, and find stomata 

 still in the middle region of the upper surface, as well as in 

 great numbers on the lower. 



We find a remarkably small amount of differentiation in 

 the chlorophyll parenchyma, considering the great expanse of 

 leaf. In this also the leaf agrees closely with miro. The middle 

 elements are only very slightly elongated, and show no signs 

 of lignification ; on the upper surface we find one or two rows 

 of wide palisade parenchyma, while the rest is composed of 

 loosely arranged irregular-shaped parenchyma. 



The vascular bundle is of great size, the phloem being better 

 developed than the wood. Transfusion tracheids are well de- 

 veloped at the sides of the bundles. 



We see by this transverse section that, of all leaves of those 

 we have studied, this leaf is the least adapted for the prevention 

 of excessive transpiration. It has the largest expanse of leaf,, 

 no sclerenchymatous hypoderm, and in addition it bears sto- 

 mata on the exposed upper surface. Taking these facts into 

 consideration, we should not be surprised that the tree has 

 endeavoured to make up for these deficiencies by a reduction of 

 its leaves in length and breadth. 



I have cut sections of various stages of reduction to see if 

 the reduction in length and breadth is correlated with any 

 anatomical changes. None of any importance occur till the 

 leaf has been very greatly reduced, and closely united to the 

 stem. The reduction in length is as great or greater in pro- 

 portion to the reduction in width. 



Reduced-scale Leaf : Free Tip. 



We note a great difference in size from the last stage. We 

 see that the margins are greatly strengthened and are curved 

 round the stem to serve for the protection of the neighbouring 

 leaves. In the middle of the upper surface we see a bulge out 

 of tissue. This is a continuation up of the region of the leaf 

 where it joins the stem. 



In the chlorophyll parenchyma we also find changes. Here 

 we find the palisade parenchyma on the lower surface and the 

 looser on the upper, instead of vice versa as in the preceding 



