AS AIDS IN THE DETERMINATION OF SPECIES. 19 



V. — Chaeacteeistics of Each Species as Deeived from the Transverse 



Sections. 



Baron von Mueller, in his " Eiicalyptograpliia," as well as in his humbler 

 " Botanic Teachings," has adopted two principal expedients for helping to determine 

 the numerous species of Eucalypts, viz., the nature of the bark and the nature of 

 the anthers, 



We now add a third, and although it has only been rigorously applied to thirty 

 different kinds, and to a few more casually, there is every reason to believe that the 

 principle will hold good throughout that extensive genus of plants. It is based upon 

 the form and arrangement of the structures revealed in a transverse section of a 

 well-developed and fully formed leaf stalk, taken in conjunction with external 

 characters of the leaf. 



While the learned Baron has given a leading place in his classification to the 

 two principles just mentioned, his fertile mind and wide knowledge have suggested a 

 number of others which he has partially applied. Thus the size of the pollen-grains 

 has been found to vary in different species, but to be more or less constant in each. 



Again, the number and distribution of the stomata have enabled him to form 

 three series — 1st, according to the presence of stomata on the under surface only 

 (hypogenous) ; 2nd, their presence on both surfaces, but less numerous above than 

 below {heterogenous); or 3rd, their presence on both surfaces, but approximately equal 

 in number above and below (isogenoiis). Then again the fruit has been suggested as 

 a basis of classification, and each of these methods has its own special advantages, 

 and its suitability for different purposes. 



The Carpologic system has this advantage, "that any species might thus be 

 defined from fruiting specimens alone, which latter, through the long persistence of 

 the fruit, are always obtainable in collecting journeys, whereas flowering specimens 

 can be got only at some period of the year, subject even to fluctuations and uncer- 

 tainties." (Euc. VIII.) 



The Cortical system is adapted " to the technic requirements of woodmen, who 

 could not be expected to enter on a discrimination of the various species from such 

 purely scientific difl'erences, on which descriptive botany would rely." (Euc. I.) Of 

 course this system likewise suits the general seeker after a knowledge of these plants. 



