Is the Eucalyptus a Fever-destroying Tree? 17 



sides.*" The stomata are on each side, and the oil cells run 

 right through. The leaves being evergreen, are performing 

 functions necessary to sustain the health and vigour of the 

 tree throughout the year. Light affects both sides alike, and 

 the temperature of the day regulates the exhalation of 

 moisture from each leaf ; and, as a light volatile body will 

 ascend with watery vapour at an ordinary temperature, the 

 oil dew exuding from each oil cell by the advancing forces, 

 is so conveyed into the air. 



The sense of smell bears ample testimony, when in gum 

 tree forests, of the presence of its volatile bodies ; for there 

 is no mistaking the aroma, as it is different from all others. 



The night and morning dews of the mallee country are 

 frequent in spring and summer ; this is in part owing to the 

 suspension of water in the air during the hot days from the 

 River Murray and its tributaries, as they pass for a con- 

 siderable distance through this scrub ; but the greater 

 amount of dew moisture is owing to the exhalation of the 

 leaves, for it must be remembered, that although the surface 

 soil is dry and hard, the roots go down to the moist under 

 soil obtained from the salt water springs. During the severe 

 droughts to which this country is subject, the trunks of 

 these dwarf trees are full of moisture, but so poor of sap 

 constituents, that in one of the species in particular, when 

 the trunk is cut close down to the roots, and placed in a 

 bushman's pannikin, a cool and refreshing draught of water 

 is obtained, to the great relief of a weary wanderer in this 

 lone and dreary scrub. 



So far our evidence of oil-evaporation may be stated 

 thus : That the desert scrub gums, after a winter of average 

 rainfall, supply the air with a continuous and even quantity 

 of aromatic vapour, and keep up a vigorous vitality through- 

 out the summer, or dry season ; and that a short season of 

 rain, and a long dry one, diminish the formation of oil, and 

 so lessen the exhalation. On the other hand, the seaward 

 species increase their quantity after a short winter. 



Next concerning the volatile acid. — Eucalyptus leaves 

 (especially those of some species) when submitted to the 

 process of ordinary distillation by steam or water for volatile 

 oil, throw off a volatile acid which greatly affects the 

 copper head of the still, so much so, that on lifting it off we 

 find the under surface covered with what is like a coat of 



* Lindley, "Elements of Botany," page 45. 

 C 



