8 THE TRANSVERSE SECTIONS OF PETIOLES OF EUCALYPTS 



With the much-debated question, whether the hard bast really belongs to the 

 vascular bundle or not, we have at present nothing to do. These bundles of bast 

 fibres always accompany the vascular tissue in these transverse sections, and while 

 they are often absent in other cases, and may be unessential, yet as a matter of 

 convenience, and without entering upon the general question, we will use the current 

 expression of fibro-vascular bundle to include the hard bast and the soft bast, as well 

 as the woody tissue. 



IV. — Sections Described Generally. 



E. globulus taken as a type. 



As each section is photographed and accompanied by its appropriate description, 

 it will only be necessary here to notice the general character of the sections. For 

 this purpose we will take Eucalyptus globulus as a type, and compare the others 

 with it. 



When an ordinary hand-cut transverse section is mounted direct in Schulze's 

 solution, the differentiation of the tissues is clearly shown. Taking a general view 

 of the section before entering into details, it is seen to be of an oval shape, one 

 and a half lines broad, by one line thick, or one and a half times broader than thick. 

 The epidermis appears as an orange-yellow, or it may be pale crimson border, edged 

 by a continuous pale yellow line, this latter indicating the presence of a cuticle. 

 Beneath the epidermis is the purple-coloured cortex, composed of cells with walls 

 varying in thickness, and as the colour indicates, of cellulose. Next comes the 

 hard bast, with its orange-yellow lignified cell walls, succeeded by the purple-coloured 

 soft bast ; then the clearly-marked bright yellow cells and vessels of the wood, 

 traversed by narrow radiating lines, composed of elongated cells of a darker colour. 

 These are the parenchymatous cells of the wood resembling medullary rays. Next 

 there is a continuation of the soft bast on the other side of the wood, succeeded by 

 the hard bast, and then the other tissues as above. In short, if we start from the 

 curve of the wood, which is more or less central, forming a woody core, there is a 

 succession of envelopes more or less thick. The soft bast surrounds the wood, and is 

 wedged in between it and the hard bast, which is surrounded in turn by the cortex, 

 and the epidermis envelopes all. 



Each of the above parts will now be specially dealt with in succession. 



1. Epidermis or Protective Tissue. — The cells of the epidermis are well-defined, 

 and distinct from the underlying tissue. It consists of a single layer of cells, 

 measuring in thickness l-670in., and the breadth of each cell on an average is 

 about l-800in. (Fig. 1, a.) 



