SPORE DISCHARGE AND DISSEMINATION 351 



lower than that for viabiht}^ of the fungus. Low temperatures usually 

 merely slow down spore production and discharge. Duller (1909) found 

 that Daedalea unicolor, Lenzites hetulinus, Polyporus versicolor, and P. 

 hirsutus discharged spores when the air temperature was 0°C. Schizo- 

 phyllum commune shed spores vigorously at 5°C., but not at 0°C. 



Andersen et al. (1947) showed that few conidia of Piricularia orijzae 

 were liberated when the host plants were dry. Continued wetting greatly 

 increased the secondary spread of the fungus in experimental trials. 

 Sporidia of rusts are formed and discharged only during periods of high 

 humidity. The need of the downy mildew fungi for changing conditions 

 of humidity has been pointed out. The hygroscopic character of the 

 capillitium of certain slime molds aids in pushing the spores to the surface, 

 where they may be disseminated by various agents. Many other species 

 of fungi appear to be independent of the air moisture, as long as there is 

 sufficient moisture in the fruit body. Gravity is believed to have little 

 effect upon spore discharge, except in the proper orientation of the fruit 

 bodies. 



The spores of some puffballs are enclosed within the nearly spherical 

 peridium, which opens by an apical pore. When sudden pressure is 

 applied to the peridium, the spores are puffed out of the pore in clouds of 

 "smoke." Gregory (1949) has shown, by use of ultraspeed photography, 

 that raindrops falling on the thin peridium of Lycoperdon perlatum cause 

 a puffing of spores (Fig. 73). The velocity of the puff as the spores 

 emerged from the ostiole was approximately 100 cm. per sec. Under the 

 conditions of the experiment, it was estimated that a drop of water falling 

 130 cm. caused the ejection of approximately 15 million spores. The 

 endoperidium and the spores inside remain dry, and the puffing is not 

 hindered, even during a rain. The impact of raindrops is believed to 

 be an important means of spore discharge from the ostiolate puffballs. 



SPORE DISSEMINATION 



Many other fungi do not have any special method of spore discharge 

 and must depend upon physical or biotic agents in nature for getting their 

 spores away from the fruit body where they are produced. Some of these 

 possess some special adaptations for dissemination by certain agents. 

 The most important agent of dissemination is air currents. The uredio- 

 spores of the rusts are not violently discharged. They accumulate in 

 the sorus and must be dislodged by the wind or movement of the host 

 plant. Many of the Monihales which produce dry conidia also depend 

 upon air movement to shake them loose from the conidiophores. Con- 

 vection currents are responsible for local spread of dry spores, while 

 splashing rain is important in the dissemination of spores with matrix. 



