Griffin. — Development of Neiv Zealand Conifer Leaves. 49 



Older Leaves. 



The leaves on plants of two to four years' growth show a 

 gradual development of cuticle and hypo-derm. In the chloro- 

 phyll parenchyma are found slightly lignified elements in con- 

 nection with the bundle transfusion tracheids, which have 

 greatly increased in number. In a plant about 2 ft. high, very 

 well developed accessory transfusion tissue was found. Mr. 

 Worsdell himself found only very slight lignification in this 

 species, but here, at this stage, there are undoubted lignified 

 walls in certain of these cells. The walls are much thickened, 

 and have pits which do not show any signs of bordered thicken- 

 ing. These lignified elements are in direct communication with 

 elements which show no signs of lignification, but which also 

 have pits on their walls. Mr. Worsdell inclines to think that 

 cells of this structure are not equivalent in function to cells in 

 a similar position in Cycas. He thinks, on account of the pre- 

 sence of simple pits, the thickness of their walls, and scattered 

 arrangements, that these elements are more of the nature of 

 stone cells, and are not used for conduction, but merely serve 

 the mechanical function of strengthening the leaf. These cells 

 do undoubtedly serve for this purpose, but I think their position 

 in direct communication with the normal transfusion tracheids 

 shows that they also serve for the equally important function 

 of carrying out water towards the margin. 



Mature Leaves. 



The leaves of the shrub and mature stages are very similar 

 in structure, but differ in arrangement on the stem. The leaves 

 of the shrub stage stand out more or less at right angles to the 

 stem, but in the mature stage they are arranged in a closer 

 spiral, and form a much smaller angle with the stem. This is 

 obviously a xerophytic adaptation. The structure of these 

 leaves does not differ greatly from the young leaf already fully 

 described. The stomata are more numerous, and are confined 

 still to the lower surface, and well away from the vascular 

 bundle, which is protected by a continuous line of hypoderm. 

 Undoubted accessory transfusion tissue was found, but the 

 cell-walls did not appear so strongly lignified as in the younger 

 stages. In the vascular bundle the number of transfusion 

 tracheids at the sides has greatly increased. A. few tannin- 

 sacs occur on the ventral side. 



Summary, P. totara. 



Summarising the principal points in connection with the 

 anatomical development, we find, — 



