85 



infected with the rust while the other plants adjacent proved to 

 be free. Nearby a few plants of Sempervivum punctatum were 

 also found to be infected with rust. 



An effort was made to determine the origin of the rusted plants 

 in the Garden. The plants of Sempervivum were obtained a year 

 earlier from a large nursery in New Jersey. In connection with 

 Dr. E. W. Olive this nursery was visited and the Sempervivum 

 beds carefully examined. It was found that a considerable 

 number of the plants of Sempervivum punctatum were badly 

 rusted. One rusted plant of S. alhernettii and one of an unknown 

 species of Sempervivum were also found. The gardeners at the 

 nursery stated that the appearance of the diseased plants had 

 long been familiar to them, although they did not know the true 

 nature of the trouble. 



While it was not possible to get exact information it appears 

 that the Sempervivum plants at the nursery were obtained from 

 Holland about twelve to fifteen years ago. Apparently the 

 disease did not attract the attention of the gardeners until two 

 or three years after the introduction of the plants. For many 

 years, however, the disease has been conspicuous in the beds and 

 many plants have been rendered worthless. Apparently the 

 disease has been more severe some years than others. 



It is perhaps surprising that this European rust should so long 

 escape observation in the United States. The fact that the 

 mycelium is perennial in the tissues of the host makes it possible 

 for the fungus to be readily distributed with the host plant. 

 The appearance of the diseased plants is also quite striking. 

 Generally the inner leaves of the rosette show the evidence of 

 infection. These elongate more than the normal and assume a 

 nearly vertical position ; they are a much paler green at the base 

 and are thickened towards the apex. The pycnidia and teleuto- 

 spore sori are developed just back of the leaf tip, not being found 

 to any considerable extent on the basal part of the leaves. The 

 pycnidia are much more numerous on some leaves than others. 

 The teleutospores germinate readily on soft agar and on the sur- 

 face of water, typical promycelia with sporidia being developed. 



