MALE FERN. SPOROPHORE. 199 



form a flat band which traverses the root longitudinally. 

 Alternating with the groups of primary xylem at the 

 periphery of the vascular cylinder are 



6. Two groups of Phloem, consisting mainly of 

 Sieve-tubes having the same characters as those of 

 the stem. Scattered among the vascular elements are 

 cells of conjunctive parenchyma. 



Note that one or two cells of tlie bundle-sheath opposite 

 the groups of xylem are larger than the rest : these are the 

 rhizogenic cells, which might have been the starting points of 

 lateral roots : the latter are formed at an early stage of develop- 

 ment of the tissues of the root, i.e., near to the apex ; if trans- 

 verse sections be made through the young part of a root, lateral 

 roots may be found in course of development in positions corres- 

 ponding to the rhizogenic cells. 



If transverse sections of the root be cut at a point not far 

 removed from the apex, it will be seen that the xylem is not yet 

 developed at the central part of the vascular cylinder, while the 

 peripheral parts may be fully formed : thus the development of 

 the xylem is centripetal, the root is diarch, and the arrangement 

 of the vascular tissues is radial. 



XV. Cut median longitudinal sections of the apex 

 of a root, which has been hardened in alcohol (of course 

 at most only one absolutely median section can be 

 obtained from a single root : it will be found con- 

 venient to embed the apex of the root in cocoa-butter, 

 or to hold it between pieces of pith or carrot). Mount 

 in glycerine, and examine first with a low power, and 

 choose out those sections in which there is a sym- 

 metrical arrangement of tissues around a single, large, 

 apparently three-cornered Apical cell, which lies at 

 some distance from the extreme apex. Note 



1. That the orientation of the apical cell is con- 



