105 



The following passages from a standard American work may be useful : — 



Young bark commonly is green, because the cortical chlorophyll is evident through the transparent 

 epidermis. Soon the stem ceases to appear green ; the chief cause of the change in colour being the develop- 

 ment of the cork layer, whose opacity makes the chlorophyll invisible. The common bark colours are 

 grey, brown, and black; but red occurs, as in some Dogwoods (Cornus), and white, as in some Birches 

 (Betula). As the tree matures the characteristic bark colour may be seen only on the young branches, if 

 the older limbs arc furrowed. 



In a few cases, as in the Mistletoe (Phorodendron flavescens), Moonseed (Menispermum), Sassafras 

 (Laurus Sassafras), and Greenbrier (Smilax rotundifolia), the relative freedom from cork formation permits 

 the green colour to remain evident longer than usual. Such green-stemmed trees as the Bamboo and the 

 Banana are in reality gigantic herbs, in which ordinary bark does not develop. 



Often the exterior and the interior of the bark are differently coloured, as in the Hemlock (Tsuga), 

 where it is black without and red within, and as in the Yellow-barked oak (Quercus tinctoria), which is 

 named from its inner bark, the outer bark giving rise similarly to the name Black Oak (Quercus Robur). 

 Bark colours, especially interior colours, often are due to the presence of various excreted products, such 

 as the Tannins. Advantages in the various colours are not to be looked for. (Coulter, Barnes, and 

 Cowles, op. cit. ii, 708.) 



Glaucousness. 



Some Eucalypts have glaucous branches, the rest of the plant being mainly 

 non-glaucous, e.g. : — E. Andrewsi, E. Consideniana, E. gigantea, E. obliqua, E. sepulcralis, 

 E. Sieberiana. This hint is sometimes useful in the forest. 



" Powder-barks," in Western Australia, are tress with smooth barks with more or 

 less glaucous appearance (they are allied to the preceding), but the glaucousness more 

 or less covers the whole of the trunk, and is so abundant that it is easily removed by 

 friction, e.g., by human clothing. Such species include — 



E. accedens ; 



E. Lane-Poolei; 



E. microtheca (of Cue), that form of the species which is abnormal in the volume 

 of its glaucousness. 



The subject is more or less bound up with that of glaucousness in leaves, and will 

 be referred to when leaves are dealt with. 



Explanation of Plates (212-215). 



PLATE 212. 



x E. algeriensis Trabut. .. 

 la. Flowering twig; 16, buds and flowers; lc, umbel of fruits; Id, fruits viewed from the top. All 

 reproduced from Bull, de la Station de Recherches Forestieres du Nord de I'Afrique, Vol. 1, Plate 12 

 (Trabut). 

 2. Juvenile leaves from No. 221, Herb. d'Algerie, received from Dr. Trabut, in National Herbarium 

 Sydney. 



x E. antipolitensis Trabut. 

 3a. Juvenile leaves; 3b, mature leaf; 3c, buds; 3d, two views of fruits. Note that the buds and fruits 

 are angled, and in threes. Reproduced from the same bulletin as E. algeriensis, but Plate xv bis. 

 G 



