EQUISETUM. SPOROPHORE. 217 



Returning to the study of the transverse sections of 

 the internode, examine them under a high power, and 

 observe 



1. The superficial cells of irregular size and shape 

 which form an ill-defined epidermis, many projecting as 

 rounded excrescences beyond the general surface : their 

 walls are thick, and show on the outer surface small 

 and irregular projections : the cell-contents are scanty. 

 Note that on the sloping sides of the ridges, and imme- 

 diately above the chlorophyll-parenchyma, Stomata 

 may be seen cut in section, and showing two Guard- 

 cells which surround the pore, and two Subsidiary 

 cells which fit closely round them : there is a large 

 respiratory cavity beneath each stoma. 



2. The sub-adjacent cells, composing with the epi- 

 dermis the band of thick-walled tissue before men- 

 tioned, have cellulose walls (blue with Schulze's 

 solution), with narrow pits. 



3. The cells of the Chlorophyll-parenchyma are 

 thin-walled, and of oblong form : the chlorophyll 

 granules are numerous and clearly marked. 



4. The remnants of disorganised cells along the 

 margins of the intercellular cavities, which show that 

 they are of lysigenetic origin : the same may be 

 observed with regard to the central cavity. 



Add a little caustic potash to the sections mounted 

 in glycerine, and then observe the cells of the bundle- 

 sheath under a high power: their radial walls will 

 be seen to show the characteristic dark dot-like 

 appearance. Passing on to the Vascular bundles, 

 their most marked constituents will be two to four 

 groups of dark-looking elements, which are Tracheides 



