EQUISETUM SPOROPHYTE 333 



thickened, pitted, inner walls : there are no stomata 

 on the ridges. 



2. That the superficial cells of the grooves are 

 shorter, and nearly square, their outer walls bearing 

 those rounded excrescences already observed in trans- 

 verse sections, while their whole surface is dotted with 

 small projections : in this part are also numerous 

 stomata, which present the characteristic appearance 

 of two concentric circles, the outer being the limit of 

 the two subsidiary cells, the inner that of the two 

 guard-cells. Note also the peculiar radiate marking, 

 which is due to irregularity of thickening of the wall 

 separating the guard-cells from the subsidiary cells. 



Treat sections similar to the above with Schulze's macerating 

 fluid (see Appendix A) for some hours, and then dry them with 

 blotting-paper, and ignite them in a spirit-lamp on platinum 

 foil, or on a cover-glass ; then treat the ash with weak acetic acid : 

 mount the residue, and examine under a high power : a skeleton 

 will then be found to remain, which represents clearly the several 

 details of structure of the epidermis above described. From the 

 treatment which the preparation has undergone it may be 

 concluded that this is a skeleton of silica. (See p. 90.) 



VII. Cut radial longitudinal sections of an internode 

 of an underground stem : wash them well with water 

 to remove as much as possible of the starch, and mount 

 some of them in glycerine, others in chlor-zinc-iodine. 

 Note successively the following tissues : 



1. The oblong superficial cells with brown walls, 

 frequently bearing unicellular hairs. 



2. The oblong cells of the cortex with cellulose 

 walls, and containing starch. 



3. The vascular bundles, which may be easily 



