VEGETATIVE KEF ROD CCTION. 233 



those bearing male organs onl)-. A similar separation of 

 sexes in the gametophytes frequently occurs when the spores 

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



A 



Fir.. 23S. 



Fig, 



239- 



Fig. 237- ~Ay the " flower " of a seed plant {Zaniia Diuric^tta). It is composed of 

 crowded sporophylls, of wliich one is represented in /->' as seen from the side. It has 

 a stalk capped Dy a hexagonal top, s. with numerous sporangia, x , on ihe under side. 

 A , natural size. t>, magnified about 6 diam. — After Karsten. 



Fig. 238. — A bit of a section of the wall of a sporangium of a horsetail, Tlie cells of 

 the outer layer thicken their walls along spiral lines. The two inner layers of cells, t, 

 become disorganized at maturity of the sporangium. Magnified 250 diam.^After 

 Campbell. 



Fig. 239. — Two spores of a horsetail (£'^?c/j'^/«;« arvense\\ one showing the elaters 

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

 After Kemer. 



