172 SEAWEEDS 



resembles Entoderma. Its thallus is densely branched , 

 and the branches eventually grow together and form 

 a continuous plate. Phwcphila and Acrochcctc are 

 small epiphytic forms on other Algae, allied to Bollo- 

 coleon, as also is Acroblaste, which grows on stones 

 and shells. The latter has both creeping and erect 

 filaments. 



The Reproductive Organs. Conjugation of gametes 

 is known in Ulothrix (as well as in Bumillcria, a 

 fresh-water genus). The gametes are formed in the 

 ordinary vegetative cells, and escape by a side open- 

 ing. They are ovate in shape, have two cilia and a 

 red spot. They conjugate in pairs, and occasionally 

 in threes, and form a zygote. (The gametes have 

 been observed to germinate without conjugation 

 after coming to rest, but the filaments are more 

 slender than those emitted by the zoospores.) The 

 zygote increases in size and its membrane becomes 

 thicker ; after a period of rest its contents divide 

 up into a number of zoospores which germinate 

 after swarming. Phmophila has gametes with four 

 cilia, which conjugate with their posterior ends. 

 Ulothrix is reproduced non-sex ually by zoospores, one 

 to four in number, produced in the vegetative cells, 

 as the gametes are. They are larger than these and. 

 have each four cilia. In Ulothrix implexa zoospores 

 are sometimes formed which do not escape, but sur- 

 round themselves with a membrane, and eventually 

 germinate after the decay of the wall of the mother- 

 cell. Chcctophora, also possesses zoospores with two 

 cilia, and these sometimes fail to escape and behave 

 like those of Ulothrix implcxa. Entodcrma, which, like 



