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FiQ. 133. Isoetes lacustris. 



A. Transverse section of stem: cr, cortex; x, i^ xylem; c, cambium; 

 a, thin- walled tissue; It, leai-traces; 6, dead tissue. 



B, C, D. Portions of A enlarged. 



E. Longitudinal radial section of sporophyll-base : v, velum; I, 

 ligule ; bb, vascular bundle; m, megaspores; t, sterile tissue. 



F. Longitudinal section through the base of a root. 



G. Transverse section of root. 



H. Transverse section of sporophyll, showing sporangium with 

 trabeculae, t; leaf-trace, (i J), and two groups of secretory cells. 

 I. A group of secretory cells enlarged. 



