81 



An intercalary oogonium is formed on the filament at any 

 place other than the apex, as a swelling which increases in size 

 until it has reached its full development when it is cut off from 

 the filament by two septa, one on either side. 



Simultaneously with the formation of an oogonium one or 

 more antheridia are developed in connection with it.* These are 

 produced either on the same hypha or on hyphfe adjacent to it. 

 The antheridia come into close contact with the oogonium and 

 keep pace with it in its development. They contain proto- 

 plasm and nuclei derived from the hyphaj, and "like the oogonia 

 are cut off by transverse walls from the remainder of the 

 filament (Fig. VI.). The oogonia and antheridia are found in 

 large numbers in all parts of the host plant. They appear to 

 be developed at first near the surface, but are afterwards 

 produced abundantly in the deeper tissues of the plant. They 

 sometimes vary considerably in size, but as a rule the oogonia 

 obtained in sections from the same piece of infected tissue do 

 not exhibit much ' variation in this respect. 



The number of nuclei present in a single young oogonium is 

 considerable, I have counted as many as 112 ; and it is possible 

 that in some oogonia there are more than this; while in others 

 the number is considerably less. The antheridia contain from 

 six to twelve nuclei each. 



The male and female organs undergo considerable clianges 

 before the cell which is to produce the new individual is per- 

 fected. These changes are somewhat complicated owing to the 

 changes which take place in the nuclei during the process. The 

 following is a description of the phenomena in question, such as 

 would be seen in fresh specimens without any special preparation. 



The most important changes take place in the oogonium. 

 Soon after the delimitation of the latter from the hypha, the 

 protoplasm contained in it begins to separate into a central 

 portion, which forms a smooth, globular body known as the 

 egg-sphere or oosphere, which becomes surrounded by a delicate 

 hyaline membrane; and an outer portion called the periplasm 

 which surrounds the oosphere and assists later in completing the 

 formation of its cell wall. The antheridium also undergoes changes. 

 It develops a tube which penetrates the wall of the oogonium 

 and comes into contact with the wall of the oosphere. A small 



