GROUPS OF PLANTS. 



19 



ridium is more or less cylindrical and contains a somewhat uni- 

 form mass of protoplasm. The antheridium bends toward the 

 oogonium and comes in contact with it, but apparently does not 

 in all cases penetrate it. Nevertheless the egg-cells develop walls 

 and become resting oospores. 

 A 



Pig. II. Species of Saprolegma, A, mycelium growing out from and surrounding 

 a dead house-fly in -a water culture; B, C, sporangia with biciliate swarm spores; D, a 

 number of odgonia containing oflspheres; E, F, odgonia and antheridia, in F the tube of 

 the antheridium having penetrated the oSgonium. — A-C, after Thuret; D-F, after 

 De Bary. 



In Peronospora^ one of the Oomycetes, the antheridium 

 (Fig. 12, n) develops a tube which pierces the wall of the 

 oogonium (Fig. 12, 0) ; the contents unite with the egg-cell, 

 after which a heavy membrane develops forming an oospore 

 which germinates when it finds a suitable host. The plants 

 belonging to Peronospora as well as related genera are destruc- 



