41 8 FUNGOUS DISEASES OF PLANTS 



striking discoloration of the leaves is produced at first, but the 

 great number of sori which may be formed eventually give a 

 light brown color to the leaf before it falls. Considerable defo- 

 liation may result, and it is stated that a shot-hole effect is 

 sometimes produced upon the almond. The fungus is much more 

 destructive in relatively moist, warm climates. It appears gener- 

 ally toward midsummer, but the most severe effects are commonly 

 in the fall. 



It has recently been determined that the aecidial stage of this 

 fungus is ALcidinm punctatum. Tranzschel was able to produce 

 the rust by inoculations from the aecidium above mentioned on 

 Anemone coronaria. These results were confirmed by Arthur 

 with the aecidium from Hepatica acutiloba. This aecidium has a 

 perennial mycelium in some of its hosts, so that this stage alone 

 is believed to perpetuate itself. 



The uredospores occur upon all hosts of the genus Prunus 

 mentioned. They are generally hypophyllous, minute, cinnamon- 

 brown, and may be so numerous as practically to cover the entire 

 leaf. The spores are light brown, generally ovate or elliptical, 

 with thickened apex. They are thickly verrucose and are pro- 

 vided with from two to three equatorial germ pores. They measure 

 20-36 x 1 4-20 \x. Paraphyses are abundant. Tranzschel deter- 

 mined that uredospores kept over winter at St. Petersburg were 

 capable of germination the following spring. 



The teleutospores generally appear in small groups among the 

 uredospores and later supplant these entirely. The pustules are 

 generally pulverulent and chestnut-brown. The teleutospores are 

 from very light to reddish brown upon the different hosts. In 

 general form they are elliptical, deeply constricted, and the two 

 cells are more or less equal, often subspherical. They separate 

 readily. These spores are provided with pointed tubercles. The 

 spores measure 32-44 x 20-26//.. The pedicels are slender, hya- 

 line, and fragile. The lower portions of these become agglutinated 

 into short columnar masses. The free portion of each pedicel is 

 usually about the length of the spore. 



