LYCOPODIUM SPOROPHYTE 277 



band of lignified tissue (brown with chlor-zinc-iodine). 

 Here and there may be found in the cortex small 

 groups of very narrow elements, having a dark appear- 

 ance : these are single vascular bundles of the 

 leaf- trace, cut through on their course from the leaves 

 to the central vascular cylinder. A sudden transition 

 is found from the inner sclerenchymatous band (c) of 

 the cortex to 



3. The bundle-sheath or endodermis, which lies 

 next to it internally. This tissue consists of two to 

 three layers of tangentially elongated cells, the walls of 

 which have a sharp contour, are not thick, and stain 

 with chlor-zinc-iodine a slightly different tint of brown 

 from the walls of the sclerenchyma : this band, though 

 it consists of more than a single layer of cells, is regarded 

 as taking the place of the endodermis, which is met 

 with in most of the Pteridophyta as one definite layer 

 of cells. 



Treat a section with sulphuric acid : the walls of this band, 

 being of a corky nature, will be found to resist its action more 

 than the rest of the tissues. Note also that the cuticle is 

 brought into greater prominence by treatment with sulphuric 

 acid, since it resists the action more strongly than the other 

 walls. 



Within this endodermis is found 



4. A cylindrical mass of vascular-tissue : it is 

 composed, as in other cases, of (a) phloem-tissues, 

 and (5) xylem-tissues, which may be distinguished 

 by their optical properties, and by their mode of stain- 

 ing with various reagents. Observe that the phloem 

 forms a series of bands which alternate more or less 

 regularly with the masses of xylem ; the latter are of 



