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A TEXTBOOK OF THEORETICAL BOTANY 



After fertilization the oosphere secretes a thick wall and is now known as an 

 oospore. The contents of the oospore undergo considerable change ; the 

 green colour disappears and is replaced by a brown or red pigment, while 

 large quantities of oil appear in the protoplasm. Such a structure is regarded 

 as a resting spore, and it may remain for a considerable time in this con- 

 dition before germinating. It is thus an extremely suitable structure for tiding 

 the Alga over a period of unfavourable conditions. 



When conditions are favourable for its germination the cell wall bursts 

 and the contents slip out surrounded by a thin membrane. It now normally 

 divides by meiosis into four monoploid cells, and from each of these a 

 flagellated zoospore is produced exactly resembling the asexual zoospores. 

 These zoospores free themselves from the membrane and swim away, giving 

 rise eventually to separate plants. 



In Oedogonium, then, we have an example of a green Alga, with an 

 advanced type of sexual reproduction as compared with Ulothrix. Its method 

 of sexual reproduction is in some respects comparable with that of the higher 

 plants, but it is peculiar in the production of nannandrous male filaments.* 



Oospore 



4 Sworm Spores 



Zoospore 



Oosphcit 



Antherozoid 



ndlum 



Oedogonium 

 Plant 



Fig. 67. — Life-cycle of Oedogotiium. 



Despite the fact that it is itself highly evolved, it is doubtful if Oedogonium 

 is related to any higher type of plant. It would appear rather that it is an 

 end line, specialized along certain directions, but not along those which 

 produced the higher forms of plant life (Fig. 67). 



bodies 



Conjugales 



The Conjugales are Chlorophyceae devoid of flagellated reproductive 

 lies Sexual reproduction is by means of amoeboid gametes. Asexual 

 * Similar dwarf male plants are found in some species of mosses. 



