Order CONJUGATE. 



This is one of the orders of the class Chlorophycese 

 (or Green Algge). The Algas comprised in the order 

 are characterised by their reproduction, which is a 

 conjugation of isogamous gametes. This conjugation 

 is a degenerate sexual reproduction, the gametes being 

 alike in form and structure, and without cilia. Non- 

 motile gametes of this nature are known as aplano- 

 gametes. The result of the conjugation is a zygospore, 

 which, after resting for a shorter or longer period, 

 produces on germination one or more new vegetative 

 plants. Motile spores are entirely wanting in all plants 

 of the order. Sometimes aplanospores (spores formed 

 without conjugation) are produced. The cells may be 

 solitary or united to form simple colonies or filaments, 



V 



which usually float freely in the water. Division is in 

 one direction only. All possess conspicuous green 

 chromatophores (chloroplasts), and pyrenoids around 

 which starch is formed. They are also remarkable 

 for the great development of the gelatinous con- 

 stituents of the cell-wall. They are found in fresh 

 water, and very rarely indeed in slightly brackish water. 

 The two European families are : 



Fain. 1. Zygnemaeese. 



Fain. 2. Desmidiacea3. 



Family DESMEDIACE^E. 



Minute unicellular Conjugate, sometimes united 

 into colonies of a more or less fragile nature. Cells 

 very variable in form, usually constricted in the middle 

 into two symmetrical halves or semicells. The cell- 

 wall in the majority of Desmids exhibits characteristic 

 surf ace -mar kings. Chloroplasts generally divided sym- 

 metrically, one in each semicell ; sometimes two to 

 six in each semicell, or only one in the entire cell. 



