Griffin. — Development of New Zealand Conifer Leaves. 61 



teresting to note briefly the further modification of each form 

 in the succeeding changes of development. 



Plant entering on Second Year. 



The anatomy of the two forms of leaves is very similar to that 

 of the younger stage, but shows an advance in the hypoderm, 

 which in both forms is better developed at the sides than in the 

 preceding stage, and in the vascular bundle, which in both forms 

 has a greater number of conducting elements. The number in 

 the rounder form is, as a rule, less than in the flattened form. 

 The transfusion tissue is well developed in both, consisting of 

 large tracheids showing transitions out from the px to the endo- 

 derm, on the other side of which are elongated parenchyma 

 cells, which at this stage show no signs of lignification. There 

 is an occasional lignified element above the px which may 

 represent centripetal xylem, kept at this period as a transfusion 

 tracheid on account of the unusual relation of the px to the 

 elongated parenchyma. The resin-canal in both is very large 

 in proportion to the size of the bundle, as will be seen from the 

 figures. 



Plants Three or Four Years Old. 



Here we see the maximum development of the flattened form. 

 Not only are the leaves on the lateral branches more flattened 

 and narrower in transverse section, but the leaves on the main 

 stems, while they keep their awl shape, are here also inclined to 

 be flattened, as can be seen in transverse section. This increased 

 •surface for assimilation will be of great service to the young 

 plant at this period, because it has now reached the stage when 

 it must struggle hard for its existence if it is to make a place 

 for itself among the other forms of vegetation. In both these 

 leaves and those on older plants we find an increase of trans- 

 fusion tissue, especially at the sides of the bundle. We also 

 find that the middle elements of the parenchyma become un- 

 doubtedly lignified, which shows that these elements, which 

 perhaps in the first place had their origin for a different pur- 

 pose, have now become specialised further for the conduction 

 of water. 



Mature Foliage. 



Here we find on both stem and lateral branches none but 

 very much reduced awl-shaped leaves about T ^ in. in length. 

 This is the general rule for the mature plants, which grow as is 

 usual in large forests. When they grow in forests, branches 

 with leaves are found only at the top, for these alone can reach 

 the sunlight, for assimilation and natural selection tend to the 

 extinction of useless organs. In more open positions, however, 



