288 EVOLUTION OF PLANTS 



Confervacese, Siphonese, and Pheeophycese, so that the 

 possession of sexual cells showing a similar grade of 

 development does not by any means necessarily imply 

 relationship. 



The origin of the Phseophycese, or brown algse, from 

 free-swimming brown flagellate organisms, is by no 

 means unlikely, and if this is shown to be the case, they 

 must be considered as a line of development parallel 

 with the Chlorophycese rather than an offshoot from 

 these. It may also be said of the red algae, that they 

 may possibly constitute an entirely independent devel- 

 opmental line, but this is less likely than in the case 

 of the Phseophycese. 



The relationships of the Fungi is still an open ques- 

 tion. Certain forms, the Phycomycetes or alga-fungi, 

 especially the water-moulds and their allies, so closely 

 resemble such siphoneous alg^e as Vaucheria, both in 

 the structure of the thallus and in the character of the 

 reproductive cells, as to leave little doubt of their 

 probable derivation from some such green ancestral 

 forms. These Phycomycetes may be said to bear 

 much the same relation to these green algse that such 

 parasites and saprophytes as the dodder and Indian 

 pipe do to their green relatives among flowering plants. 



The question of the relation of the true Fungi, or 

 Mycomycetes, to these alga-fungi, is by no means so 

 clear, although it is generally supposed that they have 

 been derived from some such forms. Some authorities 

 claim, however, that the two groups are quite inde- 

 pendent of each other, and that the line of Mycomycetes 

 has originated from chlorophyll-less plants of extremely 

 simple structure. 



