STRUCTURAL BOTANY 



kind in this manner, under such conditions as prevail 



in nature when the weather is at all dry. 



The great majority of the 

 Fungi, however, are adapted 

 to the same conditions of 

 life as the ordinary land 

 plants, on which so many of 

 them are parasitic, and this 

 implies that their reproduc- 

 tive bodies are fitted for 

 dissemination through com- 

 paratively dry air. In 

 PytMum and among its near 

 allies we can trace the steps 

 by which this adaptation to 

 an aerial environment has 

 been attained. In some 

 species of Pythium, as, for 

 example, in the species P. 

 Baryanum, which is so 

 common on Cress-seedlings, 

 it sometimes happens that 



FIG. 93.Pythium. A, branch the sporangium does not 



of the mycelium, bearing three ,, , 



zoosporangia (). Magnified lrm ZQOSpOreS at all, but 



145. B, zoosporangium (s) g row s out directly into a 



discharging its contents (6), 



which are still enclosed in the hypha, thus starting a new 



enlarged papilla but have plant ftt Qnce w i fc hout the 

 already divided to form the ' 



zoospores. Magnified 145. C, intervention of the active 



germinating oospore(^) form- aquatic cells . 

 ing an asexual sporangium (s). * 



ing an asexual sporangium (s}. 1""'^ ^^' Evidently 

 Magnified 300. (After De this allows of propagation 



taking place, even though 



there should not be water enough to float the zoospores. 

 The same thing happens in the closely-allied genus 



