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TEXTBOOK OF BOTANY 



Fig. 239. Diagrammatic representation of the sex organs of the water mold, 

 Achlija, and of their hormonal relations as indicated by arrows; an elaboration 

 of Fig. 238. Hormone A from the female mycelium (right) is essential to the 

 formation of antheridial branches on the male mycelium (left). Hormone B from 

 the antheridial branches is essential to the formation of oogonial initials on the 

 female mycelium. Hormone C from the oogonial initials is essential to the forma- 

 tion of antheridia on the antheridial branches. The direction of growth of the 

 antheridial branches is also influenced by this hormone. Hormone D from the 

 antheridia is essential to the further development of the oogonia and the forma- 

 tion of eggs within them. Finally sexual fusions result in the formation of zygotes. 

 From J. R. Raper. 



fungus, or other species of water molds, may also grow on living animals, 

 and on decaying plant and animal remains. They are at times very de- 

 structive to fish eggs and young fish. Water molds were so named before 

 it was generally known that many species of them grow in moist soils. 

 The vegetative phase consists of tubular branching hyphae within the 

 host or the substrate. 



The slimv mass of filaments on the outside of the animal is largely 

 made up of hyphae that terminate in club-shaped sporangia, within 

 which the protoplasts divide into many motile spores. After liberation 

 from the sporangium, the motile spores may undergo various changes in 

 appearance; from them new hvphae develop. Sexual reproduction begins 

 by the formation of egg cases, or oogonia, each containing from one to 



