WALLS OF SPORES IX THE UREDIXEAE 



541 



of metabolism, but it is also possible that it may protect the 

 spores, in certain species at least, from injurious light action. The 

 teleutospore-sori of Puccinia graminis, etc., are jet black in the mass 

 and thus resemble the black sporangia of Pilobolus and the black 

 spores of Coprinus and Panaeolus. Now all these black structures 

 are often exposed to strong sunlight for many weeks or months 

 before they undergo development. The sori of the Puccinia re- 

 main attached to upright grass-stems, etc., all through the autumn 

 and winter. The sporangia of Pilobolus, after being shot away 



Fig. 218. — Cronartium ribicola. a, verrucose aecidiospore 

 of Peridermium Strobi from a White Pine ; b, teleuto- 

 spore-columns on leaf of Red Currant ; c, distantly 

 and sharply echinulate uredospores, from Red 

 Currant ; c/, smooth top of a column of teleutospores, 

 from Red Currant. From W. B. Grove's British Rust 

 Fungi, b, reduced ; a, c, and d, magnification, 600. 



from a dung mass, stick to grass leaves, grass stems, etc., until 

 horses or cattle come along and swallow them ; and the spores of 

 many Coprini and Panaeoli are only successful in finding their way 

 into dung when they have settled on grass, etc., and have been 

 eaten by herbivorous animals. It is possible, therefore, that, since 

 the sori of Puccinia graminis, the sporangium of Pilobolus, and the 

 spores of Coprinus and Panaeolus must all, of necessity, be exposed 

 to sunlight for many weeks or months, the deep brown or black 

 pigment which is present in them may have a protective signific- 

 ance so far as certain rays of light are concerned. This, however, 

 is a suggestion, the value of which can only be decided by direct 

 experiment. 



The uredospores and aecidiospores are usually sculptured upon 



