AS AIDS IN THE DETERMINATION OF SPECIES. 



11 



The contents are usually of a yellowish, but in some instances of a dark-red 

 colour, readily dissolved by alcohol, and deeply stained by tincture of alkanet. But 

 if allowed to harden by keeping in water for a lengthened period, neither alcohol nor 

 ether affects them. 



Each cavity is bounded by much-compressed cells, with their flat faces towards 

 the cavity. From the appearance presented by these intercellular spaces or excava- 

 tions, they appear to be formed by the rupture and disorganisation of the cells at 

 that particular spot, and are hence of lystgenotis origin. 



In some species there are special canals, not cortical, but enclosed by the curve 

 of the wood, which will be noticed in their proper place. 



Crystals.— Crystals of the well-known octahedral form are seen in great profusion 

 scattered through the cortical cells (Fig. 3). They vary considerably in size, 

 sometimes reaching l-800in. in length, and, judging from the usual tests, as well as 

 from their crystalline form, consist of oxalate of lime. Numerous crystals, similar 

 to the above, hkewise occur in the soft bast, but they are much smaller on the 

 whole. No species examined was entirely free from crystals, although in some 

 instances they were very scarce. 



Longitudinal Section. — Although it is not the object of this paper to give a 

 complete account of the histology of the petiole, it was thought necessary to 

 examine longitudinal, as well as transverse sections, at least in one or two cases. 



A longitudinal median section of the petiole of E. globulus, taken through the 

 shorter axis of the crescentic bundle, revealed the ordinary succession of the various 

 parts. 



The epidermis, after prolonged staining with Schulze's solution, stood out as a 

 somewhat pale, lemon-yellow border. The breadth of each cell varied from l-760in. 

 to l-830in., and the length was just a little less, or about l-920in. 



The purple-coloured cortex exhibited much smaller cells towards its outer than 

 its inner portions, the hypodermal layer usually quite distinct beneath the epidermis. 

 Cortical cells adjoining the hard bast were often relatively large (Figs. 2a and b). 



The cortical cavities had the same form as in transverse section, being irregularly 

 round, or oval, or pear-shaped, and the size was about the same. Two adjoining 

 cavities were measured, one of which was l-190in., and the other l-115in, in length. 

 The F. V. B. showed the hard bast usually in two distinct layers (an outer and an 

 inner), with intervening soft bast, and the wood with its numerous spiral and annular 



