54 NATUKAL AND ARTIFICIAL INFECTION. 



completely adapted for distribution in water. Amongst the 

 higher fungi, spore-distribution almost always takes place by means 

 of wind. Insects as agents are rare, although one does occa- 

 sionally find special adaptations intended to secure their visits. 

 The spores of many fungi are forcibly ejected from the sporo- 

 carps, asci, or sporangia ; some of the many arrangements which 

 ensure this will be given in the special part of this book, others 

 will be found in the works of Zopf,^ and De Bary.- Ludwig, 

 in his text-book,^ points out that the spores of many Ustila- 

 gineae frequenting entomophilous flowers, are provided with 

 ridges and spines, which are probably an adaptation to their 

 transportation by insects; smooth-coated spores are more common 

 on leaves, stems, and organs other than the flower, and are 

 evidently distributed by the agency of wind. 



T\\v mode of distribution and infection is quite apparent in 

 many fungi. Thus in the oat-smut {Ustilago axenae), the 

 diseased ears in a field rise above the sound, so that the light 

 dusty spores are shaken out in clouds by the slightest wind ; 

 they hibernate on the earth or on straw, and germinate in 

 spring to infect the oat-seedlings at the base of the stem. 

 Equally simple is the distribution of spores and conidia from 

 one plant to another by wind during summer. Good examples 

 of this mode are the conidia of the Erysipheae, and the 

 aecidiospores and uredospores of the Uredineae. Thus, the 

 yellow spores of Clirysomyoxi rliododcndri, when the aecidia are 

 present in very large numbers on the needles of spruce, 

 may cause the phenomenon known as " sulphur-rain." It is 

 well known that this is generally due to the yellow pollen of 

 conifers caught and carried to the ground in showers of rain, 

 but E. Hartig describes a case observed by him near Achen-see 

 (Tyrol), where objects were covered by a yellow dust, consisting 

 exclusively of spores of Chrysomyxa. Spores of this kind are 

 capable of transport to very great distances, so that heteroecious 

 species can still keep up their connection even though by no 

 means near each other. 



Aecidiospores of all kinds are distributed more Ijy wind than 

 by insects. In rare cases, however, the aecidia have a sweet floral 



^Zopf, Die Pih.e, 1890, p. .349. 



= De Bary, Morpholo<iy and Biolofj;/ of the Fungi, Knglisli Edition, 1887. 



'Lehrbuch d. niederen Kryptor/amen, e.g. p. 370. 



