336 THE BASIDIOMYCETES 



also on fruits and vegetables, on fiber and forage crops, on orna- 

 mentals, and on forest and shade trees. Among all these, Ptic- 

 cinia grainims, with its varieties tritici, avenae, and secalis, is un- 

 doubtedlv the most destructive, and is world-wide in distribution. 

 Fiiccin'hi ghmiannii causes stripe or vellow rust of wheat, rye, 

 and barley throughout the pid World, and was introduced into 

 the Western Hemisphere about 25 years ago. Fiiccmia triticifja, 

 causing leaf rust and producing aecia on Thalictrum, is another 

 important rust of \\'heat. Fiiccivia coronata, the crown rust, at- 

 tacks oats and bears its aecia on Rhamnus. The common leaf rust 

 of rye, P. nibigo-vera (P. dispersa), is coextensive in range with 

 its host and bears aecia on Anchusa. Oxalis stricta serves as the 

 aecial host for corn rust, P. sorghi. This rust is widely dis- 

 tributed in North America but normally does not cause serious 

 losses. 



Among fruit rusts no other produces losses comparable in 

 magnitude to those caused by Gymnosporangium. The mono- 

 graph of Kern (1911) lists 40 species, all heteroecious except G. 

 ber?7mdianiim. None has a uredinial stage except G. nootkatense^ 

 occurring on Chamaecy parts nootkatensis. Crataegus serves as 

 aecial host for 11 species, Amelanchier for 12, Pyrus for 7, Malus 

 for 6, Sorbus for 6, Aronia for 4, Cydonia for 5, Cotoneaster for 

 2, Pourthiaea 2, and Peraphyllum, Fendlera, Porteranthus, Phila- 

 delphus, 1 each. Two species, G. juniperi-virgmianae and G. 

 globosinn, commonly attack apples in North America, and one, 

 G. yamadae, attacks this fruit in the Orient. In the United States, 

 G. chwipes is the most serious of the pear and quince rusts; in 

 Europe, G. sabinae. The foliage and also twigs of stone fruits, 

 especially peaches, cherries, and plums, are subject to attack by 

 Tranzschelia pnim-spinosae, whose aecial stage is produced on 

 Anemone, Hepatica, and Thalictrum. 



Cronarthmj ribicola, the cause of blister rust in five-needle 

 pines, is among the best known and most destructive of tree rusts. 

 Its pycnial and aecial stages appear on the trunks and branches of 

 white pines, and the uredinial and telial stages occur on the 

 foliage of currant (Ribes) and gooseberry (Grossularia). The 

 pycnial stage first appears several years after inoculation; the 

 aecial stage (peridermium) may not appear until the following 

 year. The mycelium within pines is perennial and forms annual 



