care which the author has displayed in collecting his data are worthy of admiration, and this paper will always remain a standard one with reference to the form of the cross section of the river-beds from terrace to terrace, whatever the cause of this form may be.

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Dr. Albert Heim, Professor : Neujahrsblatt von der Naturforschenden Gesellschaft auf das Jahr, 1905, Neuseeland." Zürich, 1905.

EXPLANATION OF PLATES VI-VIIA.

PLATE VI.

1. Looking south-west through the Rakaia Gorge. The terrace in the foreground has been eroded largely from solid rock, outcrops of which can be seen on its level surface in three places.

2. Upper Waimakariri. Partially truncated spur, taken from the top of another on opposite side of river-bed, which is here about three-quarters of a mile wide.

3. Looking down Rakaia River from the Gorge Bridge, showing river-bed and high terraces.

PLATE VII.

1. River Hawden, at junction with the Waimakariri, showing aggrading shingle-streams filling up the bottom of an old lake-bed.

2. Upper Waimakariri River, showing roches moutonnées and glacial terrace, near top of picture.

PLATE VIIA.

Map of part of Canterbury District.

ART. III.-The Development of some New Zealand Conifer Leaves with regard to Transfusion Tissue and to Adaptation to Environment.

By Miss E. M. GRIFFIN, M.A.

Communicated by Professor A. P. W. Thomas.

[Read before the Auckland Institute, 14th November, 1906.]

Plates VIII-X.

THE present investigations have been confined principally to species of two genera, Podocarpus and Dacrydium, both belonging to Eickler's and later to Engler's group Podocarpeæ, which by many botanists are regarded as being more or less primitive Conifers.

As far as I have been able to ascertain, the species taken as the objects of this research have not yet been investigated

with regard to the development of their leaves. In only one place have I seen the structure of any of them described. Mr. Worsdell, in his valuable paper on "Transfusion Tissue,"* has just indicated the structure of one New Zealand Conifer, Podocarpus totara, presumably of the mature leaf; but, as will be seen later, a slightly different structure has been seen in fresh material. More will also be said in connection with this paper when the origin of transfusion tissue in the Podocarpeœ is discussed.

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Another paper dealing with a similar subject is one entitled Centripetal Wood in Leaves of Conifers," by Ch. Bernard.† Unfortunately I have not a copy of this paper, but from a short summary of it which appears in the Journ. Micros. Soc. Lond., Dec., 1904, it seems that he has confined his attention entirely to the bundle, and in particular to transfusion tissue. From his results he arrives at the same conclusion as does Mr. Worsdell with regard to the origin of transfusion tissue in Conifers.

Papers dealing with the structure of other Conifer leaves seem to be very numerous, but only a very small number of them deal with leaves from the standpoint of development in a particular species. The most important work in this direction is one by Aug. Daguillon, "Recherches morphologiques sur les feuilles des Conifères," written, " pour obtenir le grade de docteur ès sciences naturelles," in 1890. Daguillon has taken for his research the leaves of some species belonging to the genera Abies, Picea, Cedrus, and Larix, and has confined himself to strictly morphological (in the limited sense of the word) considerations of their development. In dealing with the Podocarpeæ, while keeping in view the morphological aspect, I have endeavoured in each species to go a step further and to explain the development by physiological considerations. This paper of Daguillon's will be dealt with later, at the end of this thesis, where a short comparison of the morphological results obtained in these two rather widely different groups of Conifers will be given. It has been thought best not to institute comparisons with outside groups in the main part of this paper, as these would obscure the connection between the more closely allied species. The following is the summary given by Daguillon at the end of his work (a translation has been given for clearness) :

In the Abietinea (1.) The existence of primordial leaves— i.e., of leaves intermediate between cotyledon and mature leaves -is constant. (2.) The passage from the primordial form can take place without numerous transitions, as in Pinus, or by

*Trans. Linn. Soc. Lond., 1897.

† Beiheft. Z. Bot. Centralbl., xvii. (1904).

insensible transitions, as in Abies. (3.) This passage is sometimes characterized by a modification of phyllotaxis. (4.) Sometimes 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 primordial 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 parenchyma 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 transverse 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 hæmalum 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.

The drawings have all been done with the aid of a camera lucida.

CLASSIFICATION OF SPECIES TAKEN. (ENGLER.)

The leaves of this species have been chosen as an introduction to this genus on account of their simple but well-marked transitions, which all point to the greater adaptation of the maturer plant to surroundings which call for a xerophytic habit. With the exception of young plants with cotyledons, all the leaves of the different stages were gathered within not so many yards of one another.

Young Plants with Cotyledons.

The cotyledons of this species are interesting, for they remain much longer on the plant than they do in other species of this genus. They may be found on plants several inches high, which have an appreciably thick and woody stem. There is a marked development seen in the cotyledons on the older plants from those on the younger. There is a general increase in thickness of cuticle and epidermis for protection, and increase of vascular tissue for conduction. This development is best shown by a study of transverse sections of the two.

Young Cotyledon, & in. long.-The epidermal cells are protected by a fairly thick cuticle, and have well-thickened outer and side walls.

The stomata occur on both surfaces, but more on the lower than on the upper. They are only a very little sunk, and hence very little overarched by neighbouring epidermal cells. There is an air-space beneath each.

The sclerenchymatous hypoderm is not developed except just at the margins, where more protection is required.

The chlorophyll parenchyma shows rather a high degree of differentiation. At each margin of the leaf we find ordinary parenchyma, the diameter of which is the same in all directions. Below the epidermis, on the upper side of the leaf, we find cells more or less elongated at right angles to the surface,

while on the lower side there is a tendency to elongation parallel to the surface. The cells in between these two layers are elongated in the direction of the margins, which is very desirable, considering the distance there is between the bundles and from these to the margins. Here and there between these elongated cells we find ordinary parenchyma cells, which are often seen in transverse section to form lines stretching across at right angles to the elongated cells. These cross-rows probably serve for quicker communication between the upper and lower surfaces. None of the elongated cells show any signs of lignification, which cannot be expected at this stage of development.

Vascular bundles: There is no sharply marked off endodermis round each bundle; the pericycle is one or two cells thick. The protophloem forms a well-marked crescent-shaped zone of crushed elements, while the active phloem elements are arranged in three or four radial rows. The sieve-tubes at this developmental stage are long and narrow elements which still have nuclei and horizontal transverse walls. Above the phloem are the xylem tracheids. These are spiral or pitted elements, or elements with both spiral markings and bordered pits, which latter commonly occur on the oblique end walls. On the ventral side of these elements we find the protoxylem with more or less irregular and crushed spiral thickenings. At the sides of the xylem are one or two rather larger elements, the transfusion tracheids; while occasionally an element is found on the ventral side of the wood, which therefore corresponds to centripetal xylem. Sacs containing a substance with tannin reaction also occur at the sides and on the ventral side of the bundle in the pericycle. I may mention in passing that these sacs have very much the appearance of large tracheids under certain treatments, but there can be no doubt of their nature when they are treated with ferric chloride.

It is rather interesting to note the gradual decrease of tracheids in the bundle towards the apex. In a section very near the apex we find the number reduced to six or seven, whereas near the middle and base we find as many as twenty. The number of transfusion tracheids at the sides has increased, for we find groups of twos and threes against the one or two in the middle section. These elements have spiral and pitted markings, which are seen in transverse section on the slightly oblique transverse walls.

Older Cotyledon.-Transverse section: This presents typically the same appearance as the preceding section. It is characterized, however, by a much thicker cuticle and by thicker epidermal walls. The thickened hypoderm also appears along the sides here and there as one or two isolated cells. The pali