AS AIDS IN THE DETERMINATION OF SPECIES. 49 



Cortex. — Consisting of rather loose tissue. 



Crystals. — Very numerous and in clusters. 



Cortical Cavities. — Five is a common number ; sometimes very large, about 



win- 

 Wood-pattern. — Always unbroken. 



Vessels. — Moderately numerous ; distributed towards upper portion and 



middle of wood ; largest about g~ in. 

 Body of curve is thickened about middle, and the two short horns curve 

 gently and symmetrically upward and inward. 



The thinness of the epidermis, the number and relative size of the cortical 

 cavities, the loose tissue of the cortex, the hard bast of few cells, but regularly 

 distributed, the wood-pattern, and the distribution of the large and numerous vessels, 

 seemed to point to viminalis. But the specimen turns out to belong to a tree which 

 is exceedingly variable ; "so variable," as Baron von Mueller expresses it, "as to 

 change much of former ideas as regards the precincts of Eucalyptus species," and 

 therefore it would have been a mere accident to have determined it accurately from 

 the construction of the leaf-stalk alone. 



No. 6. E. punctata (determined as E. melliodora). There is a general agreement 

 between these two forms in the small size and round shape of the section, the 

 thickness of epidermis, the number and size of cortical cavities, the hard bast composed 

 of few cells, and the general features of the wood-curve. But in the former the 

 vessels of the wood are relatively few, small, and scattered ; and in the latter twice 

 the size, numerous, and equally distributed. Further, crystals are very few in 

 punctata, but very numerous in melliodora. 



It is thus shown in a practical way how the minute structure of the leaf-stalk 

 may be employed in the acknowledged difficult task of determining Eucalyptus 

 species. As might be anticipated, this structure will vary according to differences in 

 soil and climate, heat and moisture, but there is still a certain amount of constancy 

 in the internal characters which renders their aid valuable. It is not the failure of 

 the system adopted, but the imperfection of it, which prevents its wider application. 

 Taking the characters of the leaf as a whole, and not merely sections of the petiole, it 

 is believed that specific distinctions might be decided thereby. 



