4rfa OIL-GLANDS IN THE BARKS OF CERTAIN EUCALYPTS, 



evidently by the repeated division of certain meristematic cells and the subsequent 

 enlarging of the cavity, forming several rows of narrow cells round the periphery. 



The development of the gland is probably the same as occurs in the leaf 

 oil-ducts, where the early stage-s are schizogenous, subsequently becoming lysigen- 

 ous, the mature cavity being therefore sehizo-lysigenous. No very definite 

 examples of the very early stages in development were found, however, though 

 the subsequent disintegration of the innermost cell-layers may be observed in 

 older glands. 



The bark of the mature tree E. Macarthuri is typically that of a WooUybutt, 

 i.e., the outer portion is fairly compact, short-fibred and gTcy in colour, with 

 numerous interlacing ridges, in fact close in texture to the "Boxes " The outer 

 fibrous portion consists of dead tissue, but a short distance from the exterior the 

 periderm cells are living and the odour of geranyl acetate is very distinct as soon 

 as the bark is cut. On a tree about two feet in diameter the bark examined was 

 1^ inches in thickness. Oil-glands were found right up to the dry outer surface, 

 the contents being bright yellow to brown in colour; towards the cambium the 

 oil-glands were lighter in colour. Plate xlix., fig. 7 shows a transverse section 

 of the bark near the exterior, the tissue consisting entirely of secondai-y phloem. 

 The oil-glands are numerous, usually 0.10 — 0.15 mm. in diameter, and occur in 

 areas of thin-walled tissue, either isolated or in groups. The medullary rays, 

 usually only a single row of cells in width, are often forced to one side by the 

 glands. The cells immediately surrounding the cavity are narrow and similar to 

 those found surrounding the leaf oil-glands. In E. Macarthuri the zones of bast- 

 fibres are irregular in size and distribution, and numerous single fibres are 

 found. Plate xlix., fig. 8 shows a section of a portion of the bark about 10 mm. 

 from the cambium. It is evident that there are no glands whatever in this part, 

 the larger cells seen in section being the sieve tubes. A section taken about 15 

 mm. from the cambium shows the first stages in the development of the glands 

 in a position in close proximity to the medullary rays. 



In Plate xlix., fig. 9, a tangential section near the outer portion of the bark 

 (4 — 10 mm. from the exterior), it is seen that the glands are largely distributed 

 throughout broad bands of thin-walled parenchymatous tissue, corresponding in 

 position to a broad medullary ray, which is crossed by interlacing bast-fibres. 

 Although in this species there is a tendency for the oil-glands to be arranged in 

 this radial manner, in some Eucalypts the distribution is more even throughout 

 the secondary phloem tissues, whilst in E. Smithii, as pointed out later on, the 

 glands are arranged in zones which have the broader axes directed tangentially. 

 In radial section (PI. xlix., fig. 10) the relationship between the smaller cells of 

 the numerous medullary rays and the loose thin-walled tissue in which the glands 

 are usually found, is evident. 



Nature of Oil-Gland Contents. 



In small twigs of E. Macarthuri the contents of the oil-glands are soluble in 

 80 — 90% alcohol, are granular and light yellow in colour, or almost colourless. 

 In a stem of about 45 mm. in diameter the contents of the innermost glands are 

 soluble in 90% alcohol; towards the outer portion of the bark, however, the 

 contents are darker in colour and more insoluble, even 100% alcohol having no 

 effect in many cases. In the mature bark about 40 mm. in thickness, a similar 

 state of affairs is found. Within a distance of 10 mm. from tlie outside, the 

 gland contents are as a rule quite insoluble in 100% alcohol and are dark yellow 

 in colour. In the next section (from 10 mm. — 20 mm.) the contents are partly 



