﻿Halsted : Exposure and fungous Diseases 623 



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of the sori upon the plants were fully ten days old, therefore not 

 more than two weeks might have elapsed from the time when the 

 spores came to the asparagus plants to that when sori were giving 

 off their spores. The season was unusual, July being a very rainy 

 month, and the long wet period continued into August, followed 

 by hot moist weather particularly favorable for the development 

 of fungi. 



That the source of infection was the old asparagus bed is be- 

 yond question. About midway between the two beds stands a 

 house and a few trees around it, and it was observed that there was 

 less rust upon that portion of the new bed that was in line with 

 this house and the old bed. In short, there was a barrier between 

 the old bed and the new that interfered with the free passage of the 

 spores. When the surface of the rusted stems of the old bed were 

 dry and the winds blew from it towards the new bed, the spores 

 were doubtless carried in great abundance, and these spores alight- 

 ing upon the tender stems of the young shoots, encouraged by 

 hot dewy nights, quickly germinated and rusted the plants. There 

 is no reason to doubt that some of the rust spores were carried by 

 the winds to long distances and infected plants miles from where 

 they were produced. 



A single other instance may be mentioned in passing that ap- 

 pears to have escaped previous observation. The hollyhock rust 

 {Puccinia malvaceavum Mont.) is very abundant in some gardens 

 in New Jersey. The normal place for the production of the sori 

 of this rust is upon the under surface of the leaf blades, but in 

 very badly infested plants the veins and petioles of the leaves and 

 even the stem of the hollyhock bear the rust spots. The point of 

 observation is this, that when the petioles are rusted the disease is 

 confined almost entirely to the upper side. 



It is possible that here there may be a working together of the 

 exposure to the germs and the favorable meteorological conditions 

 for the development of the spores. 



As in the asparagus rust the infection is rapid, but here it is by 

 means of sporidia and not by uredospores as in the Puccinia as- 

 paragi These sporidia are borne abundantly by the leaves above 

 and might naturally drop upon the upper surface of the petioles, 

 the hairiness of which would tend to hold them. It is possible 



