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 hysterophytes 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. Nore: 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 light 
will show a green band at the water’s edge, due to the myriads 
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 soceontrtad 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, yellowish 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 are 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 flies will usually be found to be covered 
