208 



Chlorophycece 



biciliated ; they possess one nucleus and contain a single pyrenoid, 

 but as the young reticulum increases in size the pyrenoids of each 

 segment multiply rapidly. Timberlake 1 states that the swarming 

 condition of the zoogonidia can be induced by the use of a reagent 

 composed of 100 c.c. of 1 per cent, solution of iridium chloride and 

 3 c.c. of glacial acetic acid. He points out that the cell-contents 

 first break up into large multinucleated masses, which in turn 



Fig. 84. Hydrqdictyon reticulatum (L.) Lagerh., from the River Lea. A, nat. size ; 

 B, small portion of a young colony ( x 110) ; C, part of a large ccenocyte contain- 

 ing a very young colony (xllO); D, quiescent zoogonidia (x480); E, zoogo- 

 nidia which are becoming apposed to form a new colony ( x 480), p, pyrenoid ; 

 F, slightly older ccenocyte with four pyrenoids (p), x 480. 



break up into smaller masses, until each mass contains a single 

 nucleus. Reproduction also occurs by the union of isogamous, 

 4-ciliated gametes, which escape from the mother-coenocyte by a 

 lateral pore. The gametes are smaller than the zoogonidia and 

 their escape is preceded by a swelling of an inner layer of the 

 cell-wall. This inner layer ruptures the outer layers and protrudes 

 as a vesicle in which the gametes swarm. On becoming free 

 they conjugate in pairs 2 . The zygospore is globose and after a 



1 Timberlake in Botan. Gazette, xxxi, 1901, p. 203. 



2 Klebs in Bot. Zeitung, xlix, 1891. 



