THE ALG^E 189 



spores, although when germinating alone they are said to 

 produce weaker plants than those formed as the result of 

 conjugation. Otherwise there is no difference between 

 the products of sexual and asexual reproduction, for the 

 zygospore, like the solitary zoospore, gives rise directly 

 to a plant like the parent. 1 In some localities germina- 

 tion without previous conjugation appears to be the rule. 

 It is only in very few species that any form of 

 sexual process has been observed in Phseophycese. In 

 the majority of these Algre, such knowledge as we 

 have goes to show that the motile cells, whether 

 derived from unilocular or plurilocular sporangia, are 

 simply zoospores capable of directly reproducing the 

 plant. There is need for much further observation 

 before we have anything like a satisfactory idea of 

 the propagation and life-history of these plants. The 

 sporangia and zoospores are very uniform throughout 

 the Phreozoosporere, but in the vegetative structure there 

 is the greatest variation. We have chosen one of the 

 simplest examples. In other families of the group, as the 

 oarweeds (Laminarice) and their allies, the thallus attains 

 a vast size, and becomes extremely complex in anatomical 

 structure. 



TYPE XV. PELVETIA CANALICULATA 



Among the commonest and most conspicuous seaweeds 

 on the coasts of cold and temperate countries are the 

 members of the order Fucacece. The species chosen for 

 our type is distinguished from all others on our shores 

 by the position in which it grows, which is always close 



1 Recent observations have completely confirmed the occurrence of 

 sexual reproduction in Edocarpus, on which some doubt had been cast. 



