RELATIONSHIP BETWEEN OIL GLANDS AND OIL YIELDS. 149 
NOTH ON THE RELATIONSHIP BETWEEN OIL 
GLANDS AND OIL YIELDS IN THH EUCALYPTS. 
By M. B. WELCH, B.Sc. 
Technological Museum. 
[Read before the Royal Society of N.S. Wales, September 6, 1922. } 
In an examination of the leaves of various species of 
Kucalyptus it is evident that there is a great variation in 
the size and number of the oil glands, and the object of 
this investigation was to attempt to find some relationship 
between the number of glands, allowing for variation in 
size, and the actual yield of oil attained by steam distilla- 
tion. Noattempt has been made to arrive at any theoretical 
determination of what the yield should be from such an 
examination. 
In a transverse section of certain species, e.g., those of 
the Corymbosze or Bloodwood group, oil glands are not 
numerous and usually small in size, whilst in HE. terminalis 
oil glands are practically absent; on the other hand sections 
of any of the Mallee leaves e.g., H. polybractea, E. costata, 
E. oleosa, etc., show an enormous development of the 
the secretory cavities which apparently form a large pro- 
portion of the total leaf structure. Between these two 
extremes are the majority of species in which oil glands 
are developed to a greater or less extent. 
In attempting to make some comparison between the 
yield of oil by distillation and the number of glands present, 
it is obvious that certain factors must be taken into con- 
sideration. Thus two species may have in section what 
appears to be an equal development of oil glands, but on 
closer examination it is found that one leaf is thicker than 
