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 

 Pytliium 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 

 the sporangium does not 



,, , 



form zoospores at all, but 



grows out directly into a 







FIG. 93. Pythium. A, branch 



of the mycelium, bearing three 

 zoosporangia (). Magnified 

 145. B, zoo-sporangium (s) 



discharging its contents (&), 



which are still enclosed in the hypna, thus Starting a new 



plant at once, without the 

 intervention of the active 



a i atic cells - Evidentl y 



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 



enlarged papilla tyt ha 



already divided to form the 



zoospores. Magnified 145. C, 



Magnified 



300. (After De 



