ALTERNATION OF GENERATIONS IN ALG.E. 481 



such alternation, and in others again (such forms are numerous), an alternation 

 occurs, but of a character quite different from that of higher plants 



First , we will mention such as show an alternation of generations not unlike 

 ha of the Fern It will be remembered that in the Fern there is a simple pro- 

 thallium upon which the sexual organs arise, and from the fertilized egg-cell a new 

 generation, of considerable dimensions, is developed which produces asexual spores 

 these m turn giving rise to prothallia. In the group of the Red Seaweeds or 

 Flondese (cf. pp. 61, 62, and 

 figs. 204 7 and 204 9 , p. 53), the 

 seaweed plant is the sexual 

 generation and bears the rudi- 

 mentary fruits with tricho- 

 gynes and the male spermatia. 

 After fertilization, a consider- 

 able growth is initiated, which 

 results in a mass of spores 

 being abstricted, these spores 

 being in many cases inclosed 

 in a sort of capsule, which 

 develops concurrently with the 

 spores. This capsular struc- 

 ture with its spores we may 

 interpret as a very simple 

 asexual generation comparable 

 to the sporogonium of a Moss 

 or to a Fern -plant with its 

 spores. Of course this asexual 

 generation is very ill-marked 

 in the Red Seaweed, and it 

 is difficult to quite draw the 

 line between it and the sexual 

 generation of which it forms 



a continuation. It has this in common with Mosses and Ferns; that from a single 

 process of fertilization a numerous progeny of spores is begotten spores which 

 on germinating give rise to sexual plants again. 



The brown Wrack, Fucus, is an example of a Thallophyte in which alternation 

 of generations is not known to take place. In this seaweed every generation is a 

 sexual generation, and the fertilized egg-cells, so far as is known, give rise not to 

 spores but to new sexual generations. Its life-history is described and figured on 



pp. 51, 52. 



And now we come to a type of alternation of generations, prevalent amongst 

 green Algse and some families of Fungi, which seems to be quite distinct from the 

 rhythmic alternation which obtains in the Mosses, Ferns, &c. 



Fig. 353. Asexual and sexual reproduction in tne Mucorini. 



i Mycelium producing asexual spores in stalked sporangia. * A single sporan- 

 gium in section. Formation of a zygospore. 1 x 40 ; a x 260 ; x 180. 



VOL. II. 



The oft-mentioned 



81 



