94 PLANT MORPHOLOGY 



oil. I^nicelhilar and mostly solitary, rarely multicellular. Sometimes 

 naked but usually with sculptured cell walls. Nearly all free-swimming. 

 Keproduction by fission, and sometimes by zoospores, rarely by isoga- 

 metes (?). Motile cells generally with two laterally attached cilia, one 

 lying in a transverse groove. 



Xanthophyceae. Cells with yellow-green plastids containing a larger 

 proportion of carotinoids than chlorophyll. Reserve food stored as oil 

 or leucosin. Unicellular (and uninucleate), (;oenocytic, or multicellular. 

 Cell walls often absent, when present usually consisting of two over- 

 lapping halves. Reproduction by fission or by spores and isogametes. 

 Motile cells with two unecjual cilia attached anteriorly. 



Bacillariophyceae. Cells with golden-brown plastids containing an 

 excess of carotinoids over chlorophyll and storing food mainly as oil. 

 Unicellular and either solitary or colonial. Cell w^all consisting of two 

 overlapping valves, highly silicified. Reproduction by fission, auxo- 

 spores, and isogametes. Motile cells rare. 



Chlorophyceae. Cells with plastids containing a greater proportion of 

 chlorophyll than carotinoids. Reserve food usually stored as starch. 

 Unicellular (and uninucleate), coenocytic, or multicellular. Unicellular 

 forms solitary or colonial. Reproduction by fission or by spores and 

 either isogametes or heterogametes. Motile cells generally with two 

 or four cilia attached anteriorly. 



Charophyceae. Cells with plastids containing a greater proportion of 

 chlorophyll than carotinoids; usually storing food as starch. Multi- 

 cellular. Reproduction by heterogametes formed in complex multi- 

 cellular sex organs of a distinctive type. Sperms with two equal cilia 

 attached anteriorly. 



Phaeophyceae. Cells with plastids containing chlorophyll and an 

 excess of carotin and a brown pigment (fucoxanthin). Reserve food 

 occurring chiefly as laminarin or oil. Multicellular. Reproduction by 

 spores and either isogametes or heterogametes. Motile cells laterally 

 biciliate, the cilia of unequal length. 



Bhodophyceae. Cells with plastids containing chlorophyll, carotinoids, 

 and a red pigment (phycoerythrin). Reserve food stored chiefly as 

 "floridean starch." With rare exceptions multicellular. Reproduction 

 by spores and heterogametes, these never ciliated. 



GENERAL CONCLUSIONS 



The algae constitute the simplest and oldest group of green plants. 

 Their bodies are adapted, both in structure and function, to live in water. 

 Although knowledge is lacking concerning the nature of the first plants 

 to have Uved on the earth, they must have been aquatic and may have 

 been similar to some of the existing blue-green algae. These plants are 



