28 A TEXT-BOOK OF BOTANY. 



Vegetative reproduction is much like that of the higher plants, 

 through the production of root-tubers or bulbils, stem bulbils, and 

 through special branches arising at the nodes. The bulbils are 

 filled with starch and are capable of over- wintering. The sexual 

 mode of reproduction is through the activity of oogonia producing 

 oospores, and antheridia producing antherozoids or sperms. These 

 are adjacent to each other at the nodes, the oogonium forming a 

 central elliptical cell which is surrounded by a crown of cells 

 through which fertilization takes place (Fig. 13). 



PH^OPHYCE.I-:. The Phaeophyceae, or Brown Algae, are dis- 

 tinguished by having brown chromatophores. They are mostly 

 found in the colder waters of the ocean, and are either free or 

 attached to a substratum. They vary in size from microscopic 

 organisms to delicate filamentous or cord-like forms, and may be- 

 come of enormous size. Some are called rock-weeds and give the 

 characteristic color to the rocks between low- and high-tide marks. 

 Others are known as " kelps," and these grow near the low-water 

 mark. They vary in color from an olive-green to a brown. The 

 chlorophyll may be extracted by alcohol, leaving the other pig- 

 ments, phycoxanthin and phycophaein. Many of these Algae are 

 rich in iodine, being one of the sources of this element. They also 

 contain large quantities of sodium, and were used at one time 

 in the manufacture of sodium, and have been used to fertilize the 

 soil in parts of Europe as well as in New England. 



They are more complex in form than the Green Algae, and 

 are distinguished by having hold-fasts which, while not in the 

 nature of true roots, yet serve to hold the plant. They may also 

 develop stems and bear leaf-like structures of many varied forms. 

 Other-- also develop swollen bladders which contain oxygen and 

 which s L -rve to buoy up the plant. 



Fr< is, or I'.ladder Wrack, is one of the common rock-weeds 

 i I-'ig. 14. /' I. It gro\v> near the surface of the water, attached 

 to rocks, and produces a regularly dichotomously branching 

 thalhis. Some of the forms in the upper branches produce air 

 bladders which are spherical or slightly elongated and usually in 

 pairs. The margins of the branches are either entire or somewhat 

 serra- The lips of older branches become more or less swollen 

 and are termed receptacles. They are dotted over with minute 



