16 



Leaf -Scars 



and 



Lenticels. 



Internal 

 structure. 



Pith. 



latifolia these fissures cross at right angles cutting the surface 

 of the bark into small squares and producing a tessellated 

 appearance ; in other cases strips and plates, or scales, of various 

 shapes and sizes are produced. 



As the stem of a tree or shrub increases in size the outer 

 layers of bark are cast off and the way in which this is done is 

 often characteristic. In the Birch, the bark peels off, i.e. ex- 

 foliates, in rolls, in the Khair (Acacia Catechu) in long narrow 

 strips which remain for some time on the trees giving a ragged 

 appearance, and in Gmelina arborea in large, irregularly shaped, 

 scales, thus exposing patches of pale yellowish surface below 

 which contrast strongly with the grey external bark. 



18. The bark on young stems, 



on branchlets and on twigs often exhibits peculiar and 

 characteristic marks, the principal of which are the 

 so-called leaf-scars which mark the spots from which the 

 leaves have fallen, and the lenticels. The leaf -scars of course 

 follow the arrangement of the leaves and in deciduous species 

 we can at once see from the position of these scars whether 

 the leaves are opposite, alternate, whorled and so on. Their 

 size and shape vary greatly in different species. A reference 

 to Figs. 1 and 2, Plate XI, will indicate how we may readily 

 distinguish two trees (Odina Wodier and Hymenodictyon ex- 

 celsum), which, when bare of leaves, are somewhat alike in the 

 forest, by an inspection of their twigs and principally by the 

 shape and arrangement of their leaf-scars. In some cases the 

 entire leaf is not shed and the bases of the leaves persist and 

 give the stem a ragged appearance, as in species of Phoenix. 



Lenticels are interruptions in the outer coat of bark which 

 allow air to penetrate to the internal tissues and they usually 

 appear as raised corky spots, or lines, of varying shape and size. 

 In the Birch, for instance, they are horizontal lines, being very 

 large and conspicuous, while in Pyrus Pashia they are small 

 spots. They are often of a paler colour than the surrounding 

 bark and are thus made conspicuous. 



19. If now we look at the cut 



surface of that portion of our teak stem which lies inside the 

 bark we find certain peculiarities which require notice. 



In the centre there is a small area of soft tissue called the 

 pith which, in young stems, branches and twigs, is often large 

 and conspicuous. The size and shape of the pith varies in 

 different species. As a rule it is small, but in Teak it is rela- 

 tively large and conspicuous. In the Walnut and Prinsepia 

 uiilis it is divided into characteristic large chambers, In cross 



