DETAILED ACCOUNT OF SPECIFIC PLANT DISEASES 539 



telia on species of the genus. Ribes, viz., R. aureum, R. nigrum, R. 

 rubrum with which intermediate hosts (it does little damage. The 

 susceptibiHty of different currants varies considerably (Fig. 193). 



The attacked white pine trees are stunted, the tops show a bushy 

 growth and the part of the tree where the mycelium occurs is swollen. 

 The leaves of the currant infested by the fungus are thicker in texture 

 and assume a different color. The aecidia are erumpent from the bark 

 in the form of a bladder with an inflated peridium about one centi- 

 meter high and yellowish-white. The spores are roundish, or poly- 

 gonal, coarsely verrucose, orange in color and measure 22 to 29/i by 18 to 

 20/i. The urediniospores form orbicular groups surrounded by a deUcate 

 peridium which opens at the summit with a pore. They are ellipsoid 

 to obovoid in shape, echinulate, orange and their dimensions are 

 21 to 24/i by 14 to i8/i. The smooth teliospores are crowded along the 

 veins of the leaf. They are orange to brownish-yellow, 70/i long by 

 2i/i broad. 



This serious disease may be controlled by the destruction of the 

 hosts, namely, the currant and gooseberry bushes especially in the wild 

 state. This disease threatens the extinction of all the species of five- 

 leaved pines including those of the Pacific States, such as sugar pine, 

 Pinus lambertiana. 



Red-rot {Poly poms ponder osus, H. von Schrenk). — The red rot of 

 the western yellow pine {Pinus ponderosa) usually starts in the tops of 

 the "black-top" trees, i.e., trees which have been dead for two or more 

 years. At one or more points, one will find that the wood immediatelv 

 under the bark starts to rot and the rot proceeds inwardly to the wood 

 which becomes wet and soggy, and rapidly becomes brittle, so that it 

 crumbles into small pieces when rubbed. The color of the wood changes 

 to blue and later to red yellow. When the decay has gone on for 

 some time, bands and sheets of a white felty substance consisting of 

 masses of hyphae are found filling certain cracks which result, because 

 of shrinkage in the wood mass. The destruction of the wood continues 

 until the heartwood is reached. 



Red-rot is caused by a higher fungus which enters the tree through 

 beetle holes made into the dead cambium of the wood killed by the 

 "blue" fungus which precedes the red rot. When the wood has been 

 completely destroyed red-rot fungus forms its sporophores which begin 

 to grow out from the mycelium, as flesh-colored knobs, which rapidly in- 



