THE VASCULAE CRYPTOGAMS 



97 



sporangium, of which there are many, arises from the 

 growth of a little group of cells. The essential part, 

 however, can all be traced to a single superficial cell, 

 which by its repeated divisions gives rise both to the 

 archesporium and to that part of the wall lying over it. 



u.b. 



v.b. 



FIG. 44. Equisetum maximum ; part of transverse section of 

 young cone, showing one complete peltate scale, and parts 

 of two others (P). sp, sporangia ; the shaded part is the 

 archesporium ; v.b, vascular bundles ; the scattered shaded 

 cells are tannin sacs. Magnified 50 diameters. (W. C. W.) 



At the stage shown in Fig. 44 the archesporium has 

 already grown and divided up, so as to form a good- 

 sized mass of spore-producing tissue. The wall is several 

 cells in thickness. The layer of cells which immediately 

 surrounds the spore-producing tissue on all sides, and 

 may be called the tapetum, is soon used up for nutritive 

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