438 OIL-GLANDS IN THE BARKS OF CERTAIN EUCALYPTS. 



EXPLANATION OF PLATES XLVIII.—XLIX. 



Plate xlviii. 



Eucalyptus Macarthiiri. 



Fig. 1. Transverse section of 1 mm. stem showing two primary oil-glands 

 in the uppermost cortical region. The epidermis has not yet been removed. 



Fig. 2. Transverse section of 6 mm. stem showing the phloem and cortex 

 above and portion of the xylem below. Two oil-glands are seen at the top, right 

 and left hand corners, also corresponding in position and size with the primary 

 oil-glands common in the majority of young Eucalyptus stems. Although there 

 is a marked increase in the thickness of the secondary pihloem, oil-glands are not 

 yet prominent. The epidermis has been replaced by a narrow periderm layer. 



Fig. 3. Transverse section of the phloem and cortical tissues of a 10 mm. 

 stem, showing an increase in the number of secondary oil-glands. These are scat- 

 tered throughout the phloem, but occur always in conjunction with the medullary 

 rays. 



Fig. 4. Transverse section of the outer portion of a 16 mm. stem. The great 

 increase in number and size of the secondary oil-glands is prominent, particularly 

 towards the outer limit of the phloem fibres. Towards the cambium, smaller 

 glands are seen in course of development and the widening of the medullary ray 

 where the gland is incorporated is evident. 



Fig. 5. Transverse section of the outer portion of a 45 mm. stem. The maxi- 

 mum development in size is evidently at some distance below the periderm, 

 which shows practically no increase in thickness. Towards the cambium, numer- 

 ous small glands are seen in stages of development. 



Fig. 6. Radial longitudinal section of the outer portion of a 45 mm. stem. 

 The distribution of the glands in relation to the bast fibres is shown. It is evi- 

 dent that the glands are not elongated but are circular or elliptical in cross 

 section. 



Plate xlix. 



Figs. 7-10. Eiicaiyptus Macarthwi. 



Fig. 7. Transverse section of bark or secondary phloem of a mature tree 

 near the exterior. The oil-glands measuring up to 0.15 mm. in diameter are found 

 in the loose thin-walled parenchymatous tissue. Parallel to the numerous medul- 

 lary rays crossing the field from left to right are bast fibre zones. Stone cells 

 are rare in this species. 



Fig. 8. Transverse section of the bark of a mature tree within 10 mm. of 

 the cambium. There are no oil-glands in this region, the larger cells in section 

 being the sieve-tubes. 



Fig. 9. Longitudinal tangential section of the bark of a mature tree within 

 10 mm. of the exterior. Two oil-gland zones are seen, crossed by interlacing 

 bands of one or more bast fibres. 



Fig. 10. Radial longitudinal section of the mature bark within 10 mm. of 

 the exterior. Crossing the field from left to right are the numerous thin-walled 

 medullary ray cells, the oil-glands showing a comparatively even distribution in 

 this section. 



Fig-s. 11-12. Eucalyptus Smithii. 



Fig. 11. Transverse section of the mature bark passing through an oil-gland 

 ■^one. The zones in this species have the broader axis at right angles to the 

 medullary rays. The glands are especially numerous and large, measuring up to 

 0.3 mm. in diameter. 



Fig. 12. Radial longitudinal section of the mature bark. This shows a large 

 gland-bearing zone with two smaller bast-fibre zones, giving the appearance of a 

 typical tangential section. The disintegration of the large area of thin- walled 

 parenchyma in which the glands occur, helps to give rise to the extremely rough 

 outer bark found in the species. 



