the Fungi of Austin, Texas, and Vicinity 581 



of the three; it includes the effects of light, heat and moisture, 

 water especially being needed to properly develop the fructification 

 organs of fungi. 



Austin is subjected as a rule to sudden and violent variations in 

 temperature, to long periods of exceedingly hot dry weather ac- 

 companied by intense sunlight, all of which tax the vitality of the 

 higher green plants much more than that of the fungi. If the 

 quantity of moisture in the air were great it would permit some 

 species to exist here that are otherwise excluded, but the vapor 

 density in this locality is at a minimum.* These climatic forces all 

 operate to deter and limit, or even exclude many species from 

 thriving here that otherwise might be expected. These forces also 

 play an important part in the distribution and number of the para- 

 sitic species. The xerophytic character of this region causes a large 

 percentage of the native plants to protect themselves from too 

 much sunlight, heat and evaporation, by clothing their leaves and 

 other green parts with a thick, tough epidermis, with a dense 

 coating of hairs, with stomata so arranged as to remain closed, 

 much of the time, or so sunken beneath the surface as to become 

 inaccessible. The entire plant thus becomes hard, woody and im- 

 pervious. The spores, therefore, have great difficulty in ever 

 reaching the epidermis as the clothing of long, dense hairs tends 

 to catch and hold them away from the surface. The few that 

 chance to reach the epidermis and germinate are often unable to 

 pierce it with their delicate hyphae and the stomata being closed 

 or inaccessible the germ tubes cannot enter by that route. 



The spores, after finding lodgment on the epidermis, often fail 

 to even germinate from lack of sufficient moisture or the intense 

 heat and sunlight may even destroy their vitality. These facts ac- 

 count for the comparative freedom from fungal attacks of most of 

 our oaks, barberry, mesquite, cedar, etc. In the spring when the 

 leaves are young and tender and when moisture is abundant, the 



fungi may obtain a foothold and often do, or in the summer during 

 protracted rainy periods, f the spores may germinate and often do so, 



* The months of July, August, and September during the past season have been a 

 remarkable exception in possessing a high degree of humidity, which has been most 

 evident in foliage and in the development of parasitic fungi. 



t As during the past summer. 



