VEGE TA TI I 'E RETROD UC TION. 



233 



those bearing male organs only. A similar separation of 

 sexes in the gametophytes frequently occurs when the spores 

 are equal in size, as in Marchantia and horsetails, but it 



ri<;. 237. 



Fig. 237- -A, the " flower " of a seed plant (Zamia muricata). It is 1 omposed of 

 crowded sporophylls, of which one is represented in A' as seen from the side. It has 



a stalk capped by a hexagonal tup, .>. with numerous sporangia, 1 . on the under side. 

 . I , natural size. ' ti, magnified about 6 diam Aftei Karsten, 

 Fio. 23S. — A bit of a section of the wall of a sporangium of a horsetail The cells of 

 the outer layer thi< ken their walls along spiral lines. The two inner layers of CI 



become disorganized at maturity ol the sporangium. Magnified 250 diam \tt.r 



( 'ainpbell. 



I'll.. 239.— Two spores of a horsetail [Eguisetum arvense); one showing thi elaters 

 open, as when dry, the other with them coiled, as when moist. Magnified 25 diam. — 

 After Kerner. 



