40 MASS. EXPERIMENT STATION BULLETIN 202. 



concerning the disease was available to the growers. Rust causes loss in 

 at least three ways. A spike of snapdragon blossoms is useful only when 

 it is beautiful, and the rust pustules on leaves and stem considerably mar 

 the appearance and hence lessen the value of otherwise salable spikes. 

 An attack of rust impairs the vitality of the host plant, and results in 

 smaller flowers and shorter spikes than the normal. In severe cases the 

 stems and branches are girdled, causing the death of the plant. 



History axd Disthibution. 



Snapdragon rust was found in California in 1895 (Blasdale, 1903). The 

 causal organism was described in 1899 under the name of Puccima Antir- 

 rhini Diet, and Holw. (Dietel, 1899). In 1913 the disease was found 

 in Illinois, and in 1914 it was found in Ohio and Indiana (Rees, 1914). 

 By 1915 the rust had appeared in Wisconsin and Iowa (Peltier, 1919). 

 In 1915 the writer observed the disease in Maine, New Hampshire, Massa- 

 chusetts, Rhode Island and Connecticut, and it was well established in 

 New England, both out of doors and under glass. In this year, also, it was 

 reported from Oregon (Bailey, 1915). In 1916 it was reported from 

 Guelph and INIontreal, Can., and also from Alabama (Peltier, 1919). It 

 was found in Nebraska in 1916-17, and is now known to occur in jNIissouri 

 (Thurston, 1919). Snapdragon rust is evidently generally distributed 

 over the United States, more especially in the northern part. 



SYjMPTOMS. 



Snapdragon rust may occur on plants of all ages from cuttings and 

 seedlings just beginning to show foliage leaves up to mature blossoming 

 plants. A severely attacked snapdragon has a most dejected appearance. 

 The leaves hang limp and wilted as if the plant had been deprived of water, 

 the flowers open small and prematurely, and leaves and stems bear choc- 

 olate-brown powdery pustules each edged by a yellowish rmg. Leaf 

 blades, petioles, stems and calyces are attacked. Usually the lower leaves 

 of the plant are most affected. 



In the early stages there appear on the under side of the leaves swollen 

 yellow patches just inside the epidermis. These yellow patches are 1 to 7 

 mm. in diameter. At this tune the leaf may curl slightly. About forty- 

 eight hours after these yellow patches first appear the epidermis is 

 ruptured, exposing brown powdery masses beneath. These brown spore 

 masses, the uredinia, have been described as being usually circularly 

 grouped (Clinton, 1915), but according to the ^\Titer's observation this 

 circular grouping is not an especially dependable characteristic. On the 

 upper surface of the affected leaves are yellow blotches, corresponding in 

 position to the uredinia beneath. The spore powder in the uredinia is in 

 an agglutinate condition at first, but after a few days it becomes dry and 

 dusty and is easily blown about. The uredinia are not sunken. They 

 are confluent with age. The ring of ruptured epidermis surrounding a 

 uredinium is soon concealed by this brown spore powder. 



