352 PHYSIOLOGY OF THE FUNGI 



It is well known that spores of some of these fungi may be blown for 

 hundreds of miles and remain viable. 



Dissemination of the zoospores of the aquatic fungi may be accom- 

 plished locally by means of the flagella or for greater distances by the 

 movement of water, which may carry the spores both in the motile and 

 in the encysted stages. The condition of diplanetism, which involves 

 two motile stages separated by an encysted stage, may be advantageous 

 for the greater dissemination in water. The translocation of mud and 

 moist soil by means other than water may also be important. Although 

 the motility of zoospores of certain parasitic fungi, such as Phytophthora 

 infestans, can scarcely be considered an important means of dissemina- 

 tion, it does enable the spore to move short distances in a drop of water 

 on the host and facilitate penetration through stomata. 



Insects are likewise important agents of dissemination of fungus spores. 

 The insect may be attracted to spore masses by odor or color and feed 

 upon the spores, or the insect may be merely an incidental carrier of 

 spores adhering to the external parts of the body. Leach (1940) states 

 that "in the majority of cases where the question has been investigated, 

 spores have been found to pass through the intestinal tract of insects 

 uninjured." The conidia of Claviceps purpurea, being produced in sweet 

 droplets of liquid, also emit an odor which attracts insects. Similarly, 

 the stinkhorn fungi produce their spores in a malodorous matrix and are 

 frequently visited by flies. These adaptations ensure insect dissemina- 

 tion. The blue-stain fungi {Ceratostomella spp.) produce spores in sticky 

 droplets in the tunnels of bark beetles, which act as the principal agents 

 of dissemination. 



The symbiotic relationship between species of Septohasidium and scale 

 insects represents a highly evolved adaptation for the dissemination of 

 the fungus spores. Although these fungi produce basidiospores, they are 

 unlike most Basidiomycetes in that the spores are not forcibly discharged 

 from the basidium. Couch (1938) has made a comprehensive study of 

 this genus and has described the life history in detail. The fungus forms 

 a layer over the bodies of scale insects, some of which are parasitized, 

 while others are not. The uninfected female insects under the fungus 

 may produce young, many of which crawl over the sporulating surface 

 at the time of sporulation. These may become infected, crawl about, and 

 settle down some distance away. Such infected young insects are solely 

 responsible for the dissemination of the fungus. 



Spore dissemination is also unique in the Tuberales (truffles), whose 

 fruit bodies are formed entirely underground. There are no direct means 

 of getting the spores up to the air for dissemination. These fruit bodies, 

 which give off an odor, are dug up and eaten by rodents. In this process, 

 pieces of the fruit bodies are dropped, and the spores are thus disseminated. 



