1889.] BOTANICAL GAZETTE. 103 



mal layer, which in Pinus seems collenchymatous rather than 

 sclerencliymatous ; (2) in the presence of this tissue in the 

 median region between the epidermis and bundle; (3) in 

 its absence at the resin duct ; (4) in their indeterminate po- 

 sition. 



In fact, so widely variant is the system in Taxodium 

 itself, that it is only through an examination of some hun- 

 dreds of sections that even an approximate disposition is to 



be found. 



So far, therefore, as the strengthening apparatus is con- 

 cerned, the leaf of Taxodium seems much less perfectly de- 



veloped than that of Pinus. 



Between the bundle and the epidermis of the lower leal 

 surface, relatively close to the latter, is found the single resin 

 duct. The position is that to be expected from the nature ot 

 the leaf as shown by Thomas in Vergl. Anat. der Coniteren- 

 laubblatter. No accessorv passages are found in any other 

 portion of the leaf. In transverse section the duct is seen to be 

 somewhat irregular in outline, more nearly polyhedral than cir- 

 cular. The bounding cells, as above said, seem to be collenchy- 

 matous, and differ onlv in their thickening from the sur- 

 rounding parenchvma. Those cells lying between the epi- 

 dermis and the duct are the most heavily thickened, and by 

 their arrangement furnish not onlv support but protection. 



On the upper side of the duct' the collenchymatous cells 

 shade down gradually as to thickness of wall, until they 

 teach the bundle. The duct thus seems to be perfectly sup- 

 ported and protected in the vertical line. 



No marked extension of the thick-walled bounding cells 

 is to be found laterally ; they seem in that direction to pass 

 somewhat abruptly into the typical parenchyma of the meso- 



phvll (figs. 4 and 11). , 



'The secretory cells of the duct, generally six in number, 

 show in transverse section a marked difference in size and 

 form. In size, they often differ as four or five to one while 

 their forms range from irregularly triangular, through nar- 

 rowly elliptical to oval (fig. 1 1). , . 

 In median longitudinal section thev are seen to have then 

 longest diameter in the direction of the duct, while the 

 bounding cells, which show numerous intoldings, have a 

 relatively similar arrangement (fig. 10). The walls ot the 

 secretory cells are extremely thin and delicate, showing no 

 thickening in any direction. 



No 



con- 



