240 ROYAL SOCIETY OF CANADA 



{result of bleaching aa developed in the outermost cork layers, the cells 

 of which have also become devoid of contents, the whole as in the outer 

 layers of normal birch bark. it is to be observed, however, that the 

 bleached layers are not developed with uniformity over the entire surface 

 and this, in conjunction with an irregular exfoliation, produces a 

 blotched appearance due to the exposure of the underlying and brown 

 layers. Further examination also shows no evidence whatever, of lenti- 

 cels, nor are there any indications of nodal regions. It is thus to be 

 noted that, while the general aspect of the structure is such as to indi- 

 cate with certainty, its relation to the white birch, it differs from the 

 latter in the important respect that there are no lenticels. The form 

 of the growth is peculiar and points to some determining influence. The 

 entire structure is of essentially uniform width and thickness throughout 

 — that is, there is a variation in such dimensions of not more than about 

 one millimetre. The cross-section shows a narrow ellipse, the dimen- 

 sions of which are 1.0-1.1 cm. X 0.30-0.40 cm., from which it is also 

 to be observed that there is very little bulk, and that the growth was 

 of an exceedingly slender character. A transverse section discloses the 

 fact that the structure is not homogeneous, but that it is built up of a 

 series of concentric layers disposed about a central, slit-like cavity. A 

 magnifying power of ten diameters is quite sufficient to show that there 

 are from 38 to 41 such layers, that they are composed of cork tissue and 

 that they are separated from one another by a layer of absciss tissue 

 which ruptures in drying, or which is completely ruptured by the action 

 of the knife in sectioning; so that whether we look at the end of the 

 specimen, or at the section removed therefrom, the layers are quite 

 separate and distinct from each other (Fig. 1.) 



Further, microscopical examination shows that the various cork 

 layers have been disposed about a central region of parenchyma in which 

 they obviously had their origin, and it is desirable that these regions 

 should be studied in detail. The parenchymatous layer occupying the 

 central area (fig. 2, pr.) readily splits at maturity as the result of ex- 

 treme desiccation, so that it is never found entire, but its two halves lie 

 on opposite, sides of a central cavity and form layers of very unequal 

 thickness as may he seen in the photograph. Structurally, it consists of 

 rounded and very thick-walled parenchyma cells, between which there are 

 also developed numerous and often very large intercellular spaces which 

 probably represent a structural accommodation to internal aeration. 

 The size and frequency of these spaces can be understood when it is re- 

 called that in the absence of lenticels, respiration must have been carried 

 on under exceptionally difficult conditions after the cork commenced to 

 form, and towards the end of the growth it may even have become in- 



