PRINCIPAL GROUPS OF PLANTS. 



43 



The oogonia and antheridia (Fig. 21, D-F) are also formed 

 at the ends of hyphse. The oogonia are usually spherical and the 

 wall contains a number of small pores. The contents, which are 

 at first more or less uniform, later develop egg-cells, of which 

 there may be as many as fifty in a single oogonium. The anthe- 

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



FIG. 21. Species of Saprolegnia: A, mycelium growing out from and surrounding 

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

 ber of oogonia containing oospheres; E, F, oogonia and antheridia, in F the tube of the 

 antheridium having penetrated the oogonium. A-C, after Thuret; D-F, after De Bary. 



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. 



In Peronospora, one of the Oomycetes, the antheridium 

 (Fig. 22, n) develops a tube which pierces the wall of the 



