1899] MICROSCOPICAL JOURNAL. 37 



in size, so that it is difficult to obtain an idea of the av- 

 erage size. In general the cells on the ventral side of the 

 leaf are smaller than the cells on the dorsal side. The 

 mesophyll is broken by resin ducts, of which there are 

 two, fig. B, 4. Three ducts are frequently found and some- 

 times even four. The ducts are entirely surrounded by 

 parenchyma, and so may be classed among the "parenchy- 

 matous ducts." The number of the cells in the resin 

 ducts varies from ten to fourteen. A fully developed 

 duct measures, on an average, 100 mm. in diameter. 

 The resin ducts have usually only one row of sheath cells, 

 but in some ducts there are portions which have two rows 

 of cells. In addition to these cells there is a row of nar- 

 row, very thin-walled secreting cells lining the resin 

 duct. These cells are very irregular in outline, and there 

 are about half as many of them as of the larger cells. 



Fibro-Vascular Region. — The central part of the leaf 

 is occupied by the bundle region, which is surrounded by 

 a well defined endodermis. There are from fifty to fifty- 

 seven cells in the endodermis. These cells measure on an 

 average 47 mm. in width, 27 mm. in thickness, and 137 

 mm. in length. In tranverse section they are almost 

 oval in shape. The leaf has two fibro-vascular bundles 

 which are completely surrounded by a fibrous tissue. 

 The tissue which lies next to the bundle sheath is pitted, 

 but that which lies in the centre of the bundle region and 

 between the two bundles is entirely free from pits and 

 has very thin walls. Scattered in the tissue next to the 

 sheath are some cells which are free from pits. These 

 cells are rounded in shape. They have an average width 

 of 40 mm., a thickness of 38 mm., and a length of 65 mm. 

 The pitted cells are so very irregular in shape that no 

 measurements were taken of them. The thin-walled 

 cells between the two bundles are much more uniform in 

 size and shape. These cells have an average length of 

 598 mm. The vascular bundle occupies an average space 



