EVOLUTION OF SIPHONOPHYCEAE 195 



the plant body has become almost completely non-septate 

 and the sexual reproduction has become heterogamic. 

 This plant body and heterogamic generation have been 

 bequeathed to the hysterophj^tes of this line (Class 

 Phycomyceteae) , and both suffer marked degeneration 

 in passing from family to family. 



300. So also we may trace an evolutionary line from Cla- 

 dophoraceae to Valoniaceae (and Botrydiaceae), Bryop- 

 sidaceae, Dasycladaceae, and the Charales, in all of which 

 the erect, rooted and regularly branched plant body 

 becomes more and more marked. Here there is again a 

 passage from isogamy to heterogamy. 



Laboratory Studies. Note: In addition to those mentioned 

 below many marine forms, as Codium, Penicillus, Halimeda, 

 Udotea, etc., occur in warm seas, and may be studied with 

 profit, (a) Collect a quantity of Water-flannel (Cladophora) 

 and put it into a large dish of water, leaving it over night. 

 Next morning the side of the dish which is nearest to the hght 

 will show a green band at the water's edge, due to the mjTiads 

 of zoospores which escaped during the night. Mount a drop 

 of water and search for zoospores. Occasionally the escape of 

 zoospores may be seen by mounting a number of filaments and 

 searching carefully. 



(b) Collect a quantity of terrestrial Green Felt (Vaucheria) 

 and preserve it in a dish of water. After a few hours a large 

 number of zoospores may be observed collected at the edge of 

 the water nearest to the light. 



(c) Examine carefully mounted specimens of the bright green 

 filaments, and look for the thickened branches which produce 

 the zoospores. 



(d) Select some of the oldest, j'cllowish filaments. Mount 

 and examine with a low power for the sexual organs. In col- 

 lecting specimens for the study of the sexual organs it is usually 

 necessary to take those masses which arc yellowish and appear 

 to be dying or dead. 



(e) Kill a few flies in strong alcohol and place them in a dish 

 containing algae freshly gathered from some ditch or pool. 

 After a day or two the flics will usually be found to be covered 



