EQUISETUM SPOROPMYTE 331 



thin-walled, and of oblong form : the chlorophyll- 

 corpuscles are numerous and clearly marked. 



4. The remnants of disorganized 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 endo- 

 dermis 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 

 of the xylem, and are disposed, roughly speaking, in 

 the form of a V, while the apex of the Y is occupied in 

 each bundle by a large air-cavity. There are origin- 

 ally four groups of xylern elements in each bundle, two 

 bordering on the cavity, and two nearer the endoder- 

 mis; the elements of the former are often only im- 

 perfectly seen in transverse sections, since they are apt 

 to become disorganized during development. Between 

 the air-cavity and the endodermis lies a mass of 

 tissue of the phloem, with relatively thin cellulose 

 walls : sieve-plates may sometimes be observed in 

 surface view in this tissue. 



V. Compare transverse sections of the underground 

 axis, or root-stock, with those of the aerial axis : the 

 sections may be prepared in the same way as the above. 

 Note that 



1. The superficial cells have brown walls, and often 

 grow out as long, brown, root-hairs : there are no 

 stomata. 



