66 ALBUGO PORTULAC& OR A. CANDIDA. 



7. In older oogonia, more opaque bodies, the oospores formed 

 from the oospheres. Observe: 



a. Their irregular ridges on the external wall of mature 

 oospores. 



b. The contents, in younger spores. 



8. Draw some oogonia and the accompanying antheridia 

 showing different stages of development of the oospheres 

 and oospores. 



ANNOTATIONS. 



In Albugo we have a plant in some respects simple, 

 and in some quite complex. The higher development 

 is shown in its sexual elements being quite dissimilar 

 in size and behavior. The larger female organ, the 

 oogonium, receives the protoplasm of the smaller male 

 organ, the antheridium, the former remaining in a pas- 

 sive state, while the antheridium is the active agent in 

 securing the union. This is the essential plan for all 

 higher plants, as well as for some Algae, as has been 

 seen in previous work. The transfer of the protoplasm by 

 means of a fertilizing tube, and the subsequent forma- 

 tion of a thick-walled resting spore, bears a striking 

 resemblance to what takes place in Spirogyra and 

 Vaucheria. In both cases the spore clothes itself with 

 a wall which differentiates into a delicate inner layer and 

 an outer, thick, protective one. In Albugo this outer 

 wall is marked in a manner characteristic of the species. 

 The oospores thus formed remain over winter, until the 

 tissues in which they lie become disintegrated, when they 

 are distributed by rain and wind, and finally germinate. 



Next to the mode of sexual reproduction the most 



