478 OCCURRENCE OF OIL DUCTS IN CERTAIN EUCAIiYPTS AND ANGOPHORAS. 



leaves of Eucalyptiiti eximia, where medium-sized droplets appear on tlie cut 

 surface. There is apparently a break in continuity of the duet*, howevev, 

 where the petiole joins the stem. Text-fig. 3 a shows the an-angem(T.t of the 

 xylem in the young stem (left) and petiole (right), and the distribution of the 

 ducts in either case at the junction. In Text-fig. 3 b the va.scular bundles in 

 stem and petiole have joined up and, although there is no alteration in the 

 number and arrangement of the ducts in the stem, in the petiole the positions 

 of the ducts are marked only by a small quantity of .thin-walled parenchymatous 

 tissue with no cavity. In intermediate stages between (a) and (b) it is found 

 that the cavity gradually becomes smaller, being encroached upon by thin- 

 walled cells. Text-fig. 3 c shows that the "petiole" ducts have quite disappeared, 

 although as before, the ducts in the stem show no alteration. 'In Text-fig. 3 d, 

 the two ducts reappear in a corresponding position to that which they occupied 

 in the petiole, and are persistent down the stem. The non-continuity of the 

 ducts is also noticed in the very early stages of development of the leaves, and 

 will be dealt with later. 



Seedlings of several of the species were obtained and an examination gave 

 the following results : — 



E. citriodora, seedling 18 inches high. — There was no trace of ducts below 

 a distance of six inches from the hypocotyl. About 12 inches from the hypocotyl 

 the ducts were well developed, there being four in the stem and two in the 

 I)etiole and leaves. In the latter, however, they were only persistent for a 

 comparatively short distance — about 1.5 inches in a leaf 5-6 inches in length. 



E. eximia, seedling 24 indies liigh. — There was no clear evidence of ducts 

 until about 15 inches from the hypocotyl. In some leaves ducts were not found 

 in the lower portion of the petiole, but occurred nearer the leaf blade; in other? 

 the ducts were normal in arrangement, two being the usual number. 



E. truchi/phloia, seedlings 4 inches high. — There was no trace of ducts in 

 the lower part of the stem, but a single duct was found in the pith, near the 

 top. A single duct was also observed in the petiole and lower portion of the 

 Lamina in several of the leaves, which were linear-lanceolate and about 2 inches 

 in ieng'th. 



Seedlings of E. coriimbnsa and E. mcicidntn were also examined and gave 

 similar results. It is evident that these ducts do not occur in the roots or lower 

 portions of the stem, a number of seedlings being examined in this respect, but 

 witli negative results; in both cases the medulla is very sm.all. Sections of the 

 axillary stem nodules in several of the seedlings showed no trace of ducts. 



In Plate xhn., fig. 6 is seen an almost median longitudinal section of a leaf- 

 bud of E. corj/mbosa, with two outer larger leaves, and portions of younger 

 leaves and stem. Two ducts in very early stages of development are present 

 in the larger leaves and on the right are traces of stem ducts. A much en- 

 larged \new of portion of one of tiie outer leaves is shown in PI. xlvi., fig. 7. 

 The duct is here represented by a row of short ca\'ities, each separated by a 

 distinct end wall. Just above, in the same figure, is a typical gland, showing 

 its relative size and shape. It is apparent that at this .stage there is close re- 

 lationship between an individual cavity of the duct and the oil gland. In older 

 leaves and stems the end walls disappear completely, giving an elongated cavity 

 which varies in length from less than 1 mm. to 100 mm. or more in the leaves, 

 and evidently functions as a .s/ornoi? reaerrnir for the secreted oil. Two elon- 

 gated cavities or ducts are shown in Plate xlvi., fig. 5, this being an approxi- 

 mately median scctiim, parallel to the leaf surface of E. rnri/mhosa. On either 

 side of the primary vein a ntunber of oil glands in the niesophyll are also seen, 

 and it is evident that there is little in common in sliape between thoni and the 



