

411 



" Many plants possess internal glands, which often appear as translucent dots, as in the case of 

 Citrus and Eucalyptus. In most cases the glands are spherical, there being a peripheral layer of glandular 

 cells which secrete into a common reservoir. Often this structure is surrounded by a relatively impermeable 

 protective layer. Usually the reservoir does not discharge to the exterior, but in Eucalyptus and various 

 Rutaceae, there are cover cells, which after a time rupture at a definite spot, or along the walls, allowing 

 the secretions to pas3 off. The secretions secreted by internal glands resemble those secreted by glandular 

 hairs, and likewise often odoriferous." (lb. ii, 623.) 



" But little is known concerning the role of volatile oils, &c, though speculation has been abundant. 

 It has been suggested that they are of value in protecting against excessive transpiration, on the ground 

 that they absorb heat in large amount, but it is most unlikely that these oils are present in sufficient 

 abundance to check transpiration . . . Probably there is no adequate reason for believing that such 

 secretions are of any particular value in the economy of plants. Doubtless, for the most part, they 

 represent waste products, whose removal is of greater value than their retention. Any incidental gain 

 that these secretions may have probably is small." (lb. ii, 624.) 



Dawkins, A. E., has a paper " The Calculation of the Oil Content of Foliage 



from Measurements of the number and size of the Oil-glands," Proc. Roy. Soc. Vict., 



XXVIII (new series), 153 (1915). 



" The collection and distillation of oil-containing materials is often a matter involving much 

 labour. Since, therefore, the oil is well known to occur. in the case of many species in small, well-defined 

 oil-dots or oil-glands, it was thought that it might be possible to forecast the oil-content of any particular 

 species by making a few measurements of the size and number of the oil-dots, weight of leaf, &c. 



The author adopts a not complicated mathematical formula, and shows how 

 it works in the case of three Eucalypts, radiata, viminalis, Kiisoni (Kitsoniana). 

 A Leptospermum and a Eugenia are also chosen. The results are moderately close, 

 and the method is commended for further investigation. 



Now we come to two papers by M. B. Welch, B.Sc, the beginning of a broader 

 research :— - 



1. "Eucalyptus Oil Glands," Journ. Roy. Soc. N.S.W., liv, 208 (1920). 

 The author points out that the anatomy of the various parts has been little 



investigated in Eucalyptus. 



" The oil glands occur in the leaves of almost every species, but in varying number, reaching 

 perhaps a minimum in the Bloodwoods, e.g., E. tetminalis, where they are practically non-existent . . . 

 Although the distribution and number of the glands is not of very great taxonomic value, yet, as pointed 

 out in this paper, certain variations do occur and without doubt hold good throughout the distribution of 

 the species. Again, it is quite possible to recognise certain differences in their arrangement which would 

 permit of a rough classification into groups, of which some examples are given." 



2. " The Occurrence of Oil Ducts in certain Eucalypts and Angophoras " 

 {Proc. Linn. Soc. N.S.W., xlvi, 475 (1921).) 



This investigation shows that ducts formed by the linking up of short secretory cavities occur in 

 the medulla of the stems and leaves of certain Eucalypts of the Corymbose class and also Angophora 

 lanceolata. They contain oil similar in nature to that found in the leaf oil glands, and apparently function 

 as storage reservoirs. There is no direct connection between the oil glands and the oil ducts, nor are the 

 latter continuous from stem to leaf. Ducts do not occur in the roots or lower portion of the stems. 

 Apparently these ducts indicate a primitive character in those species in which they occur, and also show 

 a close phylogenetic affinity between the Eucalypts and Angophoras. 



A valuable paper, illustrated by many text-figures and micro-photographs. 



