27 



this condition of affairs that led to the recording of C. Parlatorei and C. Mac- 

 leayana as distinct species, the former species having trees placed under it, which 

 had not the long pyramidal free portion described under the latter Pine ; the 

 environment and other causes in each case, no doubt, favouring the growth of 

 each particular form of leaf. 



This decurrent portion of the leaf may be described as having three sides, 

 that is excluding the attached one, — the latter portion, adnate to the branchlet 

 not be'ng regarded as a side in this case, and the former part may be said to have 

 two concave ventral surfaces and a double convex dorsal one, or in section the 

 whole pentagonal. In the earliest leaves the junction of the dorsal and ventral 

 sides in each whorl are approximate, and at certain times touch, but as the 

 branchlets increase in circumference, the decurrent portion increases in length, in 

 some cases up to x\ inches, and, at the same time, becomes more and more removed 

 from its previous contiguous sister leaves, and remains on the stem as longitudinal 

 green stripes for an almost indefinite period. 



The maximum length probably occurs in the "Weeping Pine," and the 

 minimum in C. glauca. The decurrent portion of the leaf is very persistent 

 and retains its chlorophyll for three or four years, or even longer. 



VI. PHYLLOTAXIS. 



The arrangement of the leaves of the several species of this genus needs 

 only a few remarks, for without exception they are hqmotaxis, in regular successive 

 alternate whorls either in the spreading, horizontal, free stage, or in the decurrent 

 condition. In no instance are they spiral. Each whorl invariably consists of 

 three leaves. 



VII. HISTOLOGY OF THE LEAF. 



Here was found a new field for study, as very little if any research appears 

 to have been undertaken in the past on the anatomy of the Callitris leaf, for 

 most of the work on Conifer genera deals with material other than this Australian 

 genus. 



The part of our investigations on this organ at first presented some diffi- 

 culties, as the free ends were taken for examination, and like previous systematists, 

 we had regarded these as the true leaves. But one mm. being the maximum 

 breadth, it was found that in this small area the variety of cell structure is very 

 limited, there also being an absence of certain leaf essentials. Attention was 

 next turned to the concrescence in the search for these missing elements, and 

 there they were found. 



