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I. Sexual reproduction by isogamous gametes (isogametes), or 

 precisely similar sexual cells which undergo the process of con- 

 jugation. 



a. Gametes ciliated, known as planogametes or zoogametes, 



set free, and on conjugation forming a zygospore (or 

 zygote} (e.g. Ulotrichacea?, Ulvacese, Trentepohliaceae, 

 Pandorina). 



b. Gametes not ciliated, known as aplanogametes. 



i. Conjugation forming a zygospore which after a period 

 of rest develops directly into a new gametophyte 

 (e.g. Bacillariea? and Desmidiaceae, in which the 

 gametes are set free ; Zygnemeae, in which the 

 gametes are not set free). 



ii. Conjugation forming a zygospore which immediately 

 develops a rudimentary sporophyte with one spore 

 (e.g. Mesocarpeae). 



II. Sexual reproduction by heterogamous gametes (hetero- 

 gametes), or clearly differentiated sexual cells which undergo the 

 process of fertilization. 



a. Oogamous heterogamy : The female organ is an oogonium 



containing an oosphere. The male organ is an antheri- 

 dium in which are developed motile, ciliated antherozoids 

 (or spermatozoids). The result of fertilization is the 

 production of an oospore (e.g. Yaucheriaceae, (Edogo- 

 niales, certain of the Chaetophorales and Cladophorales, 

 and some of the Volvocacese). 



b. Carpogamous heterogamy: The female organ is aprocarp 



(consisting of carpogonium and trichogyne) with no 

 specially differentiated female cell. The male cells are 

 non-ciliated spermatia (or pollinoids}. Fertilization 

 results in the development of a cystocarp (or sporocarp) 

 with contained spores known as carpospores (e.g. 

 Rhode >phyces?.). 



The sexual organs of those Algas with similar sexual cells are 

 termed gametangia. If the Alga? are unicellular then the cell 

 itself becomes the gametangium (e.g. Desmidiaceae, Bacillariese), 

 and in the multicellular and ccenocytic forms the ordinary vegeta- 

 tive cells become the gametangia (e.g. Zygnemaceae, Chastophorales, 



