298 DISEASES OF FIELD & GARDEN CROPS. [en. 



compared with the anther and its pollen. In the process 

 of growth the antheridia naturally come into contact 

 with the oogonia, just as an anther may touch a stigma. 

 When this contact takes place the antheridium projects a 

 fine tube into the walls of the oogonium till the oosphere 

 within is touched and pierced. Some of the vital mate- 

 rial from the antheridium then very slowly passes through 

 the tube, mingles with the protoplasm within the oosphere 



and fertilisation, and the 

 formation of an oospore is 

 the result. Just as in 

 flowering plants an ovule 

 becomes a seed after fertil- 

 isation, so the oosphere 

 becomes an oospore or rest- 

 ing-spore after the contact 

 of the antheridium with 

 its contents. 



An antheridium in con- 

 tact with an oogonium is 

 farther enlarged to 1000 

 diameters in Fig. 131, to 

 more clearly show the beak 

 or fecundating tube in the 

 act of piercing the oogonium 

 and its contained oosphere. 

 By careful watching under 

 the microscope, the granu- 

 lar protoplasm from the 

 antheridium may be seen 

 to pass very gradually into 

 the oosphere. The oogonium originates by the con- 

 tained protoplasm in the mycelium congregating in certain 

 positions, generally at the ends of, or within the mycelial 

 branches, the end of the branch becomes distended with 

 vital material, and a bladder is formed, which is speedily cut 

 off by a septum or joint, as at A, Fig. 131. In many in- 



FIG. 131. Peronospora infestatis, 

 Mont. Oogonium and antheridium. 

 Enlarged 1000 diameters. 



