REPRODUCTION 177 



the breaking up of the asci, the spores lie loose in the 

 interior of the perithrecium and are liberated by the 

 rupture of the fragile wall of the latter." 



In this example the conjugation embraces two ele- 

 ments not only belonging to the same individual, but 

 also to the same mycelial filament. 



Among the algae same interesting forms of conjuga- 

 tion of elements derived from the same parent may also 

 be observed. Thus, in Ulothrix zonata sexual and 

 asexual reproduction may be seen. The asexual repro- 

 duction is accomplished by swarm spores each of which 

 is provided with four cilia. These are formed, so far 

 as can be determined, by any cell in the filament of which 

 Ulothrix is composed, and having escaped through an 

 opening in the side of the cell are immediately ready 

 to swim away and start a new growth resembling the 

 parent. The sexual reproduction is accomplished 

 through gametes which closely resemble the swarm spores 

 except that they are smaller and possess but two fla- 

 gella each. These likewise escape through an opening in 

 the lateral wall of the parent cell, but proceed to con- 

 join, forming zygotes or fertilized cells, which draw in 

 the flagella, become spherical, surround themselves with 

 a cell wall and enter upon a period of rest, after which 

 they divide into a number of swarm spores which in turn 

 escape from the capsule and swim away to found new 

 plants. In case the gametes are unable to conjugate, 

 they may behave like the swarm spores and themselves 

 found new individuals. 



Here, therefore, we find a plant with such loose methods 

 of reproduction that even its gametes or sexual cells 

 may under certain conditions fail to conjoin, but carry 

 out a parthenogenetic development i.e., germination 

 without conjugation or fertilization. 



Another interesting and instructive example is found 

 in the self-conjugation of Vaucheria which might be 

 likened to a form of hermaphroditism or bisexual nature 

 of one individual. Here we have a filamentous alga 

 whose terminal cell becomes specialized into a sporan- 

 12 



