SECT. n. 



ZYGNEMA. 



217 



take part in it at once. The cells that are opposite to 

 one another put out little protuberances, which come 

 into contact with each other ; the intervening partitions 

 disappear, so that a tube is formed which establishes a 

 free communication or passage between the cavities of 

 the conjugating cells. In the genus Mesocarpus and 

 others, the conjugating cells pour their endochromes 

 into a dilatation of the passage that has been esta- 

 blished between them, and it is there that the matter 

 mingles to form a spore or embryo cell. But in the 



Fig. 21. Conjugation of Zygnema qnininnm : A, two filaments in the first 

 conjugation ; B, completion of the act of conjugation. 



of 



Zygnema (fig. 21), which is the commonest form of these 

 plants, the endochrome of one cell passes entirely over 

 into the cavity of the other, and within the latter the two 

 endochromes coalesce into a single mass, round which a 

 firm coat is developed, and it becomes a spore. All the 

 cells of one filament are thus left empty, while spores are 

 formed in all the cells of the other. 1 Sometimes cells in 

 the same filament conjugate, and occasionally the endo- 

 chrome in a cell divides into two parts, each of which 

 becomes a spore. 



Some of the spores are quiescent, others have cilia and 

 are motile, but both after a time become attached at 

 one end by two or three root-like fibres, and grow into 



1 The Microscope.' By Dr. Carpenter. 



