136 PRACTICAL BOTANY. 



the branching filaments of Vaucheria. In the methods of 

 reproduction the resemblance is also striking. The asex- 

 ual reproduction is by the formation of zoospores or zoogo- 

 nidia, which develop in special cells that become cut off 

 from the rest of the filament by transverse partitions. 

 The zoospores are flagellated and swim about in the cell 

 in which they are formed before they are liberated by the 

 decay of the cell wall. They are then set free and swim 

 about in the water for a time. They finally develop into 

 new filaments of the plant. 



The sexual reproduction is as follows : Globular oogonia 

 are developed at the extremities or at points along the 

 sides of the branches. The antheridia are borne on the 

 extremities of small branches that develop just below 

 the oogonia. (Fig. 74, d and e.) The antheridia pene- 

 trate the oogonia, but the actual transfer of antherozoids, 

 or of protoplasm in any form, into the oogonia has never 

 been observed. The egg cells are believed to be fertilized 

 parthenogenetically, i.e., without receiving the contents 

 of the male elements. The fertilized eggs are discharged 

 and grow into new plants. 



Parasites that grow on pond scums, Desmids, Dia- 

 toms, and other fresh-water plants, are related to the 

 Saprolegriiese, as also are parasites that may be found 

 on the Plantain, the Mints, the Evening Primrose, and 

 some leguminous plants. 



References for Reading. Vines' "Text-Book of Botany," pp. 293, 

 294 ; Goebel's " Classification of Plants," pp. 96-99 ; Cooke's " Intro- 

 duction to the Study of Fungi," pp. 233, 234 ; Bennett and Murray's 

 " Cryptogamic Botany," pp. 332-334 ; Bessey's " Essentials of Botany," 

 pp. 136-139 ; Carpenter's " The Microscope," p. 569. 



CLASS IV. The Sac Fungi (Ascomycetes). The dis- 

 tinguishing feature of this class is the formation of spores 

 in sacs or asci. These sacs are club shaped or globular. 

 The class is a large one and includes many common plants, 



