most clearly at A, and is seen in greater 

 detail in pi. iii., fig. 1. A similar tissue 

 was observed in all sections of the stem, 

 even those near to the base (see pi. iii., 

 fig. 2, which is a portion of pi. ii., fig. 1, 

 enlarged). 



LX 



Microscopic Structure. 



A microscopical examination of the 

 leaf base shows that it is bounded by 

 layers of cellulose fibres. The epidermis 

 is strongly sclerized except for occa- 

 sional thin-walled cells, which show 

 large granular nuclei. Except for these 

 cells there is no tissue of a glandular 

 nature in the leaf base, and even if 

 these cells be unicellular epidermal 

 glands it is very doubtful if they 

 could secrete the quantity of resin 

 found about the stems, especially 

 when it is remembered that at the 

 lower end of the stem the leaf bases are 

 dead and even decayed away, while it 

 is there the resin sheath is thickest. 



A careful examination of the peri- 

 pheral region of the stem was therefore 

 made, this region having shown, as 

 mentioned above, a point of special in- 

 terest. Text fig. 2 represents a trans- 

 verse section of the outer layers of the 

 stem taken near the base. Below the 

 investing layer of resin are several 

 lavers of parenchyma cells showing 

 large granular nuclei. Still deeper is 

 a wide parenchymatous region contain- 

 ing numerous cells with raphides. This 

 region passes into a broad zone of 

 cambium cells, which is succeeded 

 internally by the ground parenchyma 

 of the stem through which the vascular 

 bundles run. 



The development of secondary meri- 

 stemsis rare in monocotyledonous plants, 

 but it is found in a few genera of the 

 Liliaceae, to which family Xanthor- 



rhoea belongs. In these cases the 



Fig-, z. __ _ e 



Diagrammatic transverse section of stem extending from region of mevistem 

 outwards to the resin layer. For further description see accompanying text. 



