14 Is the Eucalyptus a Fever-destroying Tree ? 



No eucalypts exceed the amygdalina, and no vegetation 

 contains so much volatile oil in the leaves as is found in 

 most of the species just named. The eight species 1 have 

 just given, not only represent the oil yield from the 

 minimum to the maximum, but also the volatile acid and 

 the tannate gum resin, as well as locality, from mountain to 

 desert. 



First, then, concerning the volatile oil. If we break up a 

 leaf of any of the eucalypti during any part of the year, its 

 usual aroma is present, and the oil cells appear the same in 

 condition, but when submitted to a practical test the quantity 

 is found to vary. Soil or locality does not appreciably 

 affect the quantity obtained from a species when operated 

 upon during the same season of the year. 



The range of those species represented in the viminalis 

 and odorata as yielding oil sparingly is limited in comparison 

 with those producing larger supplies; these have a wide 

 range. 



Gum trees when in full vigour have a large amount of 

 leaf surface, and it is necessary to note that the variableness 

 of the supply of oil does not arise from any diminution of 

 leaves on the branchlets during any part of the year. The 

 oil variation throughout some years is under 20 per centum, 

 and in others it varies very considerably, as we shall see 

 presently. Then again the variation does not follow in a 

 c\ 7 cle of time from its maximum to its minimum, but is 

 intermittenfc. To account for these peculiarities with exact- 

 ness, is a task I shall not attempt ; still, I may point out 

 that the root habit of a species, the temperature of the 

 ground, and that of the air, have much to do with it. 



For example, the eucalyptus amygdalina is a tree varying 

 in size from that of an ordinary willow to that of the giants 

 of the forest, some being over 350 feet in height; it occupies 

 chiefly the higher portions of undulating forest land, and the 

 sides of ranges, and does not extend over 100 miles inland ; 

 the ground where it grows retains a little moisture through- 

 out the summer months, September to April, the roots run 

 chiefly lateral, and are seldom lower than three feet from the 

 surface ; they are surrounded with a soil evenly cool, but 

 the temperature of the air has its usual summer range; during 

 these months the supply of oil from week to week is very 

 even, but as the cooler or winter months approach, the 

 ground becoming moist from rain, and the temperature of it 

 and the air lower, the supply of oil falls off 



