cambium is concerned with the formation of new vascular 

 bundles. It has clearly no such function here. Certain 

 monocotyledons also develop a peripheral cork cambium, but 

 the meristem tissue in Xanthorrhoea cannot have that function 

 since there is a zone of living tissue outside it, nor does any 

 part of the stem yield the characteristic reactions of suberin. 

 The purpose of the meristem seems, therefore, to be to add 

 to the cortical cells lying outside it. But*the cortical zone does 

 not increase appreciably in thickness as the stem gets older. 

 If, then, the cambium adds to it on the inside, it is clear that 

 cells must be sloughed on the outside. 



A careful examination of the outermost region of the 

 cortex, at the point at which it abuts on the resin zone, shows 

 that the layer of delimitation is irregular. The cortex cells 

 here have large granular nuclei and have every appearance of 

 secretory- cells. In many cases they show large amounts of 

 plastic contents, the nature of which could not be determined. 

 There is no recognisable epidermis to be seen. 



Text fig. 3 is a camera lucida drawing of a portion of this 

 region, and shows that the cells are not only in contiguity 

 with the resin along an irregular line, but that similar cellular 

 structure to the outer cortex cells can be discerned embedded 

 in the resin. The inference, therefore, is that the resin is 

 formed chiefly as an intra-cellular secretion of the peripheral 

 cells of the stem which are thus cut off. The cortex, however, 

 is replenished by the activity of the cambium mentioned above, 

 so that it does not diminish in thickness. Physiologically, the 

 resin may serve to cement the persistent leaf bases together 

 so protecting the stem from injury, the persistent armour 

 of leaf bases taking the place of the bark of most plants. 

 Even if the leaf bases decay away there is left a layer of resin, 

 as at the base of the trunk investigated, protecting the living 

 parenchyma of the outer cortex. 



Examination of the Resin Residues. 



It is well known that the resin is completely soluble in 

 alcohol, also in KOH solution. If, however, it is formed as 

 an intracellular secretion the walls of the cells themselves 

 should be found in the resin and left as a residue when the 

 latter passes into solution. A large number of fragments of 

 apparently pure resin from different parts of the plant were 

 examined as follows. The resin was removed as completely 

 as possible with absolute alcohol and the residue examined 

 in cedar-wood oil. In the majority of cases the resin gave 

 a. residue that showed fragments of cellular tissue similar in 



