238 



A TEXTBOOK OF THEORETICAL BOTANY 



zoosporangium in which the contents do not divide into separate zoospores 

 but germinate by a germ tube. In Cystopus we see how one stage in the 



Fig. 229. — Cystopus candidus. Asexual reproduction. A, Zoosporangium. B, Septation ot 

 zoosporangium. C and D, Discharge of zoospores. E, Flagellated zoospores. F, G and 

 H, Germination of zoospores. {After de Bory.) 



process of conidiospore formation may have been evolved by abstricting 

 these zoosporangia in chains. 



Sexual Reproduction 



The sex organs are developed in the intercellular spaces of the host tissue 

 and very often in the deeper layers of the stem. They consist of oogonia 

 and antheridia. The oogonium is globose and is developed from a terminal, 

 or occasionally from an intercalary swelling of a hypha. The mature 

 oogonium may contain as many as a hundred nuclei, together with a 

 quantity of food material. It is finally cut off by a septum from the rest 

 of the hypha. The antheridium is club-shaped and is developed in close 

 association with the oogonium. It is also multinucleate, containing some 

 twelve nuclei, and it is also separated from the supporting hypha by a septum 

 (Fig. 230). At this stage the nuclei in both the oogonium and antheridium 

 simultaneously undergo one nuclear division. 



At about the time when the antheridium comes into contact with the 

 oogonium the protoplasm of the latter undergoes differentiation, leaving a 

 zone of rather translucent periplasm surrounding the denser oosphere, 

 which contains most of the nuclei. At the point of contact of the antheridium 

 and the oogonium the antheridial wall becomes very thin and the oogonium 

 pushes its way in, forming a slight protuberance, which is called the receptive 

 spot. It appears to be functionless, for shortly afterwards there develops 



