Geiffin. — Development of New Zealand Conifer Leaves. 45 



insensible transitions, as in Abies. (3.) This passage is some- 

 times characterized by a modification of phyllotaxis. (4.) Some- 

 times marked by a change in the epidermal surface. (5.) Nearly 

 always accompanied by the development below the epiderm of 

 one or more sclerenchymatous layers, which afford the leaf 

 protection and support. (6.) The pericyclic sclerenchyme, which 

 encloses more or less completely the median vein, acquires a 

 considerable development. Further, among the two sorts of 

 elements of which it is composed (cells with bordered pits and 

 fibres with smooth membranes), the latter are often absent 

 from the primordial leaves, appearing with the passage from 

 the primordial to the definite form. (7.) In certain genera 

 (Abies and Pinus) the fibro-vascular system of the median 

 vein, proceeding from a single bundle of the stem, bifurcates 

 in the interior of the adult, while it remains simple in the pri- 

 mordial leaf. (8.) In all cases the number of conducting elements 

 of the xylem and of the phloem augments when the primordial 

 passes into the mature leaf. (9.) When foliar parenchyma is 

 heterogeneous and bifacial the differentiation of the palisade 

 parenchvma is generally accentuated in the adult leaves. 



Before proceeding to the main part of the work, it might 

 be as well to add a word or two about .the material used, and 

 its preparation for sections. In all cases the leaves have been 

 obtained directly from nature in different localities round about 

 Auckland. As far as possible, only plants growing under 

 exactly the same environment have been used for the different 

 developmental stages. 



The sections from which most of the drawings have been 

 made were cut by hand. It was found impossible to get very 

 good results from material imbedded in paraffin and cut by the 

 microtome. The great thickness of the epidermis and hypoderm 

 no doubt largely accounts for this — in the first place making 

 penetration hard during imbedding processes, and in the second 

 place causing an obstruction to the razor, especially in trans- 

 verse sections. By stripping off the epidermis and hypoderm 

 good results were obtained by the microtome in longitudinal 

 sections (radial and tangential) of the vascular bundle in the 

 cotyledons of two species of Podocarpus. 



The method of double-staining with haemalum and saffranin 

 has been found the most convenient and differential. Sections 

 treated thus have been supplemented by others which have 

 been mounted straight in a mixture of glycerine, alcohol, and 

 saffranin. These sections are much less likely to have become 

 distorted, while the saffranin marks off well such tissues as are 

 lignified. 



