36 



BOTANY. 



The sexual organs are formed on special branches, and their arrange- 

 ment is such as to make the species instantly recognizable. 



The first sign of their development is the formation of a short branch 

 (Fig. 21, A) growing out at right angles to the main filament. This branch 

 becomes club-shaped, and the end somewhat pointed and more slender, 

 and curves over. This slender, curved portion is almost colorless, and is 

 soon shut off from the rest of the branch. It is called an " antheridium," 

 and within are produced, by internal division, numerous excessively small 

 spermatozoids. 



As the branch grows, its contents become very dense, the oil drops 

 especially increasing in number and size. About the time that the 

 antheridium becomes shut off, a circle of buds appears about its base 

 (Fig. 21, B, og.). These are the young oogonia, which rapidly increase 

 in size, assuming an oval form, and become separated by walls from the 

 main branch (O). Unlike the antheridium, the oogonia contain a great 

 deal of chlorophyll, appearing deep green. 



When ripe, the antheridium opens at the end and discharges the sper- 

 matozoids, which are, however, so very small as scarcely to be visible 



except with the strongest lenses. They 

 are little oval bodies with two cilia, which 

 may sometimes be rendered visible by 

 staining with iodine. 



The oogonia, which at first are uni- 

 formly colored, just before maturity show 

 a colorless space at the top, from which 

 the chloroplasts and oil drops have dis- 

 appeared (Z>), and at the same time this 

 portion pushes out in the form of a short 

 beak. Soon after the wall is absorbed at 

 this point, and a portion of the contents is 

 forced out, leaving an opening, and at the 

 same time the remaining contents con- 

 tract to form a round mass, the germ or 

 egg cell (Fig. 21, E, o). Almost as soon 

 as the oogonium opens, the spermatozoids 



collect about it and enter ; but, on account of their minuteness, it is almost 

 impossible to follow them into the egg cell, or to determine whether several 

 or only one enter. The fertilized egg cell becomes almost at once sur- 

 rounded by a wall, which rapidly thickens, and forms a resting spore. As 

 the spore ripens, it loses its green color, becoming colorless, with a few 

 reddish brown specks scattered through it (F). 



IV 



FIG. 22. A, non-sexual repro- 

 duction in Vaucheria sessilis. 

 B, non-sexual spore of V. 

 (/eminata, x 50. 



