HYGROSCOPIC MECHANISM IN MYXOMYCETES 119 



Water as a vector of fungi. Water may sometimes serve as 

 an important agency for dissemination of fungi, although there 

 is a dearth of direct data on this point. Rain splash is known to 

 be responsible for the spread of conidia of apple bitter-rot 

 (Glomerella rufo-maculans), cotton anthracnose (G. gossypii), 

 bean anthracnose (Colletotrichiim lindemiithiamim) , and brown- 

 spot needle disease of pines (Systremma acicola). The conidia 

 of these fungi and of many others are produced in a matrix that 

 is corneous when dry but that dissolves when moist. Such fungi 

 are adapted for distribution at times favorable for spore germina- 

 tion and infection. Others are mechanically transported by dews 

 or rains and thus find lodgment on new substrata. In Colorado 

 years ago Cercospora beticola was found to be present in water 

 in irrigation ditches and to be spread to non-infected beets by 

 irrigation. Arthur (1929) mentions an outbreak of Puccinia 

 sorghi on Oxalis in a corn-field that was overflowed. 



STRUCTURAL ADAPTATIONS FOR EXPULSION OF SPORES 



At maturity or soon thereafter the spores of many species of 

 fungi are forcibly discharged. Expulsion of spores from the 

 structures within which they are delimited or upon which they 

 are borne must be regarded as a device to further the geographical 

 distribution of the particular species. 



HYGROSCOPIC MECHANISM IN MYXOMYCETES 



Within the sporangia of certain slime molds, notably Trichia 

 and Hemitrichia, the capillitial threads are thickened in spiral 

 bands. When the sporangial wall is ruptured as the result of dry- 

 ing, the tangled capillitia may be noted to be interspersed among 

 the spores. As the capillitia dry, they writhe and twist by virtue 

 of the unequal thickenings of the wall. As the ends of the 

 threads spring free, they fling adhering spores into the air. This 

 behavior is, therefore, quite like that in the liverwort, Marchantia, 

 and is very efficient in conjunction with air currents in causing 

 the spores to be widely disseminated. Dissemination of other 

 species, however, appears to be wholly fortuitous. 



The mechanisms involved in spore discharge are quite different 

 and need not indicate phylogenetic relationships. 



