EUPHYCOPHYTA 



109 



jacent cells fuse, the contents of one cell passing through a pore in 

 the intervening cell wall . 



The last phase to be described is that of zygotic contraction 

 which is brought on by further action of the contractile vacuoles, 

 after which a thick three-layered wall develops around the zygote. 



Fig. 61 Zygogonium ericetorum. A Zygnema stellinum, cell and 

 nucleus before division ( x 500). B, the same, after division 

 ( X500). C, Zygogonium^ stages in conjugation. m=male nucleus, 

 p = conjugation process. D, terrestrial form ( x 1065). E, aplano- 

 spores formed from drying up of filament ( x 542). (A, B, after 

 Cholnoky; C-E, after Fritsch.) 



the middle layer or mesospore frequently being highly sculptured. 

 The zygospore occasionally germinates almost at once, thus pro- 

 ducing plants that account for the autumn maximum, but it is 

 usually dormant until the following spring. Meiosis takes place 

 when the zygote germinates and four nuclei are formed of which 

 three abort, the plants thus only exhibiting the haploid generation. 

 A two-celled germUng is formed, the lower cell being relatively 



