222 PROCEEDINGS OF SECTION D. 



With regard to the first character above — reduction of leaf surface 

 — it is extremely common, and in all degrees of completeness up- 

 to complete loss of leaves. In the following natural orders it is- 

 very noticeable : Dilleniacege, Rutaceas, Euphorbiaceae, Legu- 

 minosas, Myrtaceas, Santalaceae, Proteaceae, Thymeleae, Epacrideae, 

 and Coniferas. The leaves may be of normal shape but very small,. 

 or may be needle-like (some Hakeas) cupressoidal [Exocarpus, 

 Callitris), spinescent, phyllodineous, or dissected {Trachymene, 

 Petrophila, Isopogon, Lomatia, Actinotits). Where the leaves are 

 mere vestiges {Casuarina) or entirely absent [Viminaria, Sphoero- 

 lohium) the work of photo-synthesis is done by the stems in the 

 earlier stages of growth. Sections of these show that the histo- 

 logical characters of leaves are assumed by these stems. 



In Bossicea the stems ai'e flattened ; in Amperea, Exocarpus,. 

 Callitris, Omphacomeria, Leptomeria and Choretrum they are angular, 

 and in Sphcerolobmm and Viminaria they are round. Seedlings of 

 the latter plant bear small elliptical leaves, the earliest broadly 

 elliptical with short petioles, and the later leaves very narrow with 

 long petioles. Then the switch-like branchlets grow out of the 

 centre. Seedlings of Bossicea scolopendria also have elliptical leaves 

 growing alternately on narrow branches. Sometimes in a wet 

 season the ordinary flat branches produce leaves. 



The second character — diminution of intercellular spaces— is 

 very marked in microscopic sections of the leaves and stems of all 

 these plants ; and the third — the augmentation of vessels and 

 sclerenchyma — is a notable feature, particularly in the leaves of 

 Hakeas and Banksias. The veins frequently show a great deal 

 of thick walled fibre, and in the needle bushes there are radial 

 columns of sclerenchyma. See paper on the structure of the leaf of 

 Banksia serrata,^ 



The palisade tissue is usually much modified. As Schimper 

 points out, the cells are greatly lengthened, but in addition there 

 are often two or three rows of cells. This is best seen in the flat- 

 leaved Hakeas, Lomatia, Eucalyptus, etc. 



Almost every plant shows a remarkable thickening of the outer 

 wall of the epidermis, which is in some cases as thick as the palisade 

 cells which it covers. In many plants there are two or three layers 

 of epidermal cells. In that case only the outer wall is thickened, the 

 inner one being rather below the normal in thickness. 



The sinking of the stomates is a very common feature. The 

 most usual method is not so much a sinking of the stomates as a 

 protection afforded by the rolling backward of the edge of the leaf. 

 This is well seen in Boronia ledijolia, Ricinocarpus pinifolius, Banksia 

 ericifolia, B. spinulosa, and many of the Legumino?ae. The midrib' 

 fills up nearly all the space between the two edges of the leaf, so that 

 there are only two narrow slits running the whole length of the leaf. 

 These are defended by hairs growing in the grooves. The hairs are 

 thick-walled and tapering to a sharp point. In some there is a 

 bulbous base to the hair, and it is remarkable that this form of hair 

 occurs in rolled leaves of plants belonging to widely separated. 



