96 



SCIENCE 



[N. S. Vol. XXIX. No. 733 



taceae, and a dozen or so related families. 

 This phylum has been unusually pro- 

 ductive of other phyla of primary and 

 secondary rank, and elsewhere^ I have 

 hazarded the suggestion that from the 

 lower Protophyceae (near Protococcoideae) 

 a phyletic line passed off and gave rise to 

 the animal kingdom. 



Springing from the filamentous Pro- 

 tophyceae is the third phylum — 



3. Zygophyceae, in which the sluggish 

 cells easily separate, and the non-ciliated 

 gametes move feebly. This is a phylum on 

 the down-grade, and all of its members 

 show structural degeneration. In the 

 desmids and diatoms the filaments usually 

 separate early into single cells, resulting 

 in the so-called "unicellular" structure of 

 these plants. 



The filamentous pondscums {Spirogy- 

 raceae, Zygnemataceae and Mesocarpa- 

 ceae) are here held to have given rise 

 by early fragmentation to several secon- 

 dary phyla, including the three families 

 of desmids, and the many families of 

 diatoms. 



From the filamentous Protophyceae there 

 came also the fourth phylum— 



4. Siphonopliyceae, in which the domi- 

 nant idea is the development of eoenocytes. 

 The retention of the typically motile cili- 

 ated gametes producing simple zygotes 

 upon uniting, the chlorophyll-green ehro- 

 matophores, and the mostly filamentous 

 or upright plant body which is rooted 

 below, are important secondary characters. 



Beginning with the segmented Clado- 

 plioraceae two secondary phyla may be 

 recognized — one {Vaucherioideae) of fila- 

 mentous plants— the other {_Bryopsidoi- 

 deae) of upright and branched plants. 



• " The Structure and Classification of the Lower 

 Green Algje," in Trans. Am. Mic. Society, Vol. 

 XXVI., 1905, pp. 121-136; and later in "A, Syn- 

 opsis of Plant Phyla," 1907. See also my " Essen- 

 tials of Botany," sixth edition, 1896, pp. 137-8. 



Many species have degenerated into hys- 

 terophytes. 



Again, from the filamentous Protophy- 

 ceae came the fifth phylum — 



5. Phaeophyceae, in which the dominant 

 feature is the addition of the brown pig- 

 ment (phycophaein) to the chlorophyll of 

 the cells. The typically motile, ciliated 

 gametes, producing simple zygotes upon 

 uniting, and the filamentous to massive 

 plant body, rooted below, are secondary 

 limiting characters. 



Starting with the filamentous and often 

 small Ectocarpaceae, this group readily di- 

 vides itself into two well-marked secondary 

 phyla — Phaeosporeae, and Cyclosporeae, 

 the former culminating in the gigantic 

 Laminariaceae, and the latter in the highly 

 developed Sargassaceae. 



Going back again to the fertile group 

 of the filamentous Protophyceae, we find 

 the origin of the sixth phylum — 



6. Carpophyceae, whose dominant char- . 

 acters are the reddish pigment (phycoery- 

 thrin) added to the chlorophyll of the 

 cells, and the growth of the zygote into a 

 spore-fruit. The mostly erect, symmet- 

 rically branched and basally-rooted plant 

 body, and the definite attainment of heter- 

 ogamy, afford important secondary char- 

 acters. 



Here the typically marine Bangioideae 

 and Florideae dominate the phylum, and 

 these develop phycoerythrin in their cells, 

 while the green fresh-water Charoideae 

 constitute a small side line. 



From the more primitive, probably fila- 

 mentous Carpophyceae came the seventh 

 phylum — 



7. Carpomyceteae, whose dominant idea 

 is the abandonment of the holophytic 

 habit, and the adoption of the hystero- 

 phytic habit, with the disappearance of 

 chlorophyll, resulting in the atrophy of the 

 vegetative portions of the plant body and 

 the increase in reproductive structures. 



