14 THE TRANSVERSE SECTIONS OF PETIOLES OF EUCALYPTS 



3. Hard Bast. — This tissue is very easily recognised in transverse section from 

 its position and structure. It forms an irregular, interrupted ring of exceedingly 

 tliick-walled cells. It passes not only round the outside of the bundle on its lower 

 surface, but curves round the upper surface, and after dijDping towards the centre of 

 the bundle, and forming a thickened mass, it continues in a graceful curve. 



Treated with Schulze's solution, the bright, yellow girdle is made to stand out in 

 bold relief. 



The hard bast, which has received various other names, such as sclerenchyma, 

 bast fibres, prosenchyma, kc, is one kind of mechanical or supporting tissue — a 

 skeleton in fact. This particular kind of tissue may occur elsewhere than in this 

 region, wherever, indeed, a strengthening of the parts becomes necessary, but in 

 order to prevent confusion the name of hard bast or bast-fibres will invariably mean 

 with us the skeleton accompanying, supporting, and protecting the soft bast. 



4. Soft Bast. — The soft bast, all but completely enclosed by the hard bast, is a 

 ring of tissue immediately adjoining and surrounding the wood. It consists of cells 

 of much smaller diameter than those of the hard bast, and relatively thin-walled. 

 In a section treated with Schulze's solution, this tissue is strikingly shown as a 

 purple patch, between the bright yellow of the hard bast on the one hand, and that 

 of the woody tissue on the other, which it completely envelopes as with a mantle. 



The thin-walled cells, many of them with large cavities, and all with cellulose 

 walls, have evidently a different function from that of the hard bast. The soft bast is 

 composed of two main elements — the cambiform cells and the sieve-tubes, both of 

 which have already been dealt with in considering the longitudinal section^ 



5. Woody Tissue. — The wood forms the central figure of the section, and with 

 its graceful infolding at each side gives rise to characteristic patterns. It sometimes 

 resembles the inverted volute of an Ionic capital, or simply a capital o lying flat, or 

 to change the figure, when, with Schulze's solution, the radiating lines are made 

 to stand out dark upon the yellow back-ground, it resembles a caterpillar coiled up at 

 either end, with its body divided into numerous segments by beaded ringS; When 

 the two horns curve round the central canals, as in E. inaculata, there is something 

 of an owl-like appearance about it, when viewed upside down. 



In a section treated with Schulze's solution it is easy to resolve the woody tissue 



into three elements — 



(a.) Wood fibres. 



(b.) Wood parenchyma. 



(c.) Vessels. 



