491 



The operculum therefore often (perhaps always) consists of two layers or 

 sub-opercula, the outer operculum of calycine origin, and the inner operculum corolline. 



One of the opercula is scarious or membraneous; this varies with different 

 species ; as a rule it is the outer one which is thin, and, generally speaking, it is 

 deciduous at an early stage, and hence it is not often observed. 



Following are examples of the 



(a) Thin outer operculum — E. microtheca, E. microcorys, E. rostrata, E. 



brachyandra. " Species generally," (Bentham, Mueller, Naudin). 



(b) Thin inner operculum — E. maculata, E. eximia, E. peltata, E. W atsoniana, 



E. terminalis, E. Abergiana, E. Preissii. " Species few," (Mueller). 



The scales of E. brachyandra shown at Qe (two figs.) Plate 127, cover the 

 operculum. In some cases they are uniform in size and show a keel or external rib. 

 They are, however, usually irregular in shape, and are doubtless the five portions of 

 an outer or double operculum covering a single bud, and have become torn by the 

 growth of the bud (See Part XXX, p. 223). Since the above was written, it has been 

 ascertained that the scales form an entire outer operculum in younger buds. It may be 

 desirable to study this, as an illustrative example of the organ. This outer operculum 

 is remarkably membraneous, and particularly at the top and also at almost regular 

 intervals around it, it sometimes shows a microscopic ribbing or thickening in places, 

 sometimes more evident in the process of drying. With the expansion of the bud, the 

 operculum being thinner (more membraneous) at the top, splits downwards between 

 the thickenings (ribs or nerves ?) into almost equal lanceolate parts, which sometimes 

 show a nerve-like vein in the middle. The splitting up of the operculum does not 

 appear to affect the growth of each part, as it continues to grow for some time 

 afterwards. The attachment at the base is sufficiently strong enough to allow for 

 this until the whole operculum is pushed off by the further development of the bud. 



In E. microtheca the outer operculum seems to split up in an opposite manner, 

 that is, from the base upwards, which indicates that the dome or top of the operculum 

 is the strongest part (least membraneous). 



E. eximia. When the petaline or corolline operculum is seemingly not present 

 (as in the case of E. eximia, for example), it would appear that it is completely fused 

 into the calycine operculum. The only alternative is that some species are acorolline. 

 This would not be without analogy, for we have in other genera a similar occurrence 

 just as we have in Eucalyptus a variation in such characters as stamens arranged in 

 bundles and also in an unbroken or staminal ring, or again in the differences as to 

 shape, texture, &c, in the calyx, and still further in the morphology of the anthers. 



I believe that the double operculum (i.e., two opercula) will be found in all 

 species, but it is very early deciduous in most. I have found the scar in very many. 



