260 PROCEEDINGS OF THE AMERICAN ACADEMY 



gelatinous, while the spores upon their surface germinate with great 

 rapidity. This germination consists in the growth of certain hyphai 

 {promycelia), which in turn bear laterally one or more, usually four, 

 secondary spores, known as sporidia ; or simply break up by the for- 

 mation of transverse partitions into spore-like bodies having a similar 

 function. These sporidia are then carried by the wind, often very 

 considerable distances, until they come in contact with certain PomecB 

 which furnish conditions for the further development of the fungus. 

 In case these conditions are not supplied, the production of secondary 

 sporidia serves as a further means of dissemination. 



Having fallen upon a proper host, the sporidia produce the next 

 phase of development by germinating, and entering the tissues of its 

 leaves, fresh shoots, or fruit. A slight discoloration of the part af- 

 fected ensues, followed by the production of flask-shaped cavities 

 opening upon its surface known as spermoffojiia, within which are 

 formed minute bodies, the spennatia, of doubtful function. These 

 spermogonia are usually accompanied by bright orange discoloration s, 

 and by the secretion of a viscous saccharine substance attractive to 

 insects. 



The next step in development consists in the formation of cecidia, 

 which appear upon the under surface of the leaves directly opposite 

 the spermogonia, or in the same position with them if the part aifected 

 is a young shoot or fruit. The secidia are cup-shaped bodies, within 

 which numerous spores are produced successively, being pushed out 

 in a mass surrounded by a membranous envelope, the peridium. By 

 the rupture of this membrane the spores escape, and, carried by the 

 wind to a proper host, produce upon it the Gymnosporangia from 

 which they were originally derived. This completes the round of 

 development, which may be summarized as follows : the Gymno- 

 sporangia on cedars produce spores (teleutospores), and these in turn 

 produce sporidia, which, flilling upon various Pomece, result in the 

 formation of a Roestelia, producing a^cidial spores, which serve to 

 reinfect the cedars with Gymnosporangia. 



To trace this connection directly by actual experiment under test 

 conditions was the object of the present cultures, and for this purpose 

 seedlings and older plants of the following species were employed, viz. : 

 Cratcegus tomentosa and coccinea, Pyrus mains, arhutifolia, and Ameri- 

 cana, with Amelanchier Canadensis. The plants were potted in most 

 cases before the leaves were developed, towards the end of April, and 

 kept in my rooms in Boston until the middle of July, at which time 

 the more important results of the experiments had been reached. The 



