5IO Journal of Agricultural Research voi. xix, no. lo 



upper part of normal sporidia. Another short tube is shown in figure 46. 

 This bears a branch with an enlarged end resembling a sporidium. A 

 constriction at the point of the first bend in the branch would give rise 

 to a fairly normal sporidium. Figure 48 shows a similar branch, but 

 this time it arises from a very long germ tube. An unbranched tube 

 is shown in figure 54. The diameter of the distal end of this tube is 

 much less than that of the average diameter of germ tubes. Such a 

 decrease in diameter frequently accompanies cross-wall production, 

 branching, and other indications of an attempt at the production of 

 sporidia. Figure 52 shows a tube with a branch of small diameter and 

 one cross wall. The end cell has broken away from the remainder of the 

 tube. 



It must not be supposed that abnormal promycelia are uncommon in 

 cultures of the short-cycled orange-rust or in cultures of germinating 

 teliospores in general. Abnormal promycelia much like those described 

 above have occasionally been found in cultures of the short-cycled rust. 

 They are not common, however, under ordinary conditions of germina- 

 tion. In cultures of the aeciospores of Gymnoconia, on the other hand, 

 most of the promycelia produced are abnormal. 



The production of promycelia by the aeciospores of Gymnoconia 

 interstiiialis seems to the writer to be strong evidence that a close genetic 

 relationship exists between the two orange-rusts. One of them is a 

 typical short-cycled rust. It produces three kinds of spores : Spermatia, 

 aeciospores, and sporidia. So far as the writer has observed it possesses 

 one and only one life cycle. There is nothing unusual about this rust. 

 The other orange-rust is long-cycled, but it is not a typical long-cycled 

 rust. It is unusual in that it possesses two life cycles. In addition 

 to the long cycle there is a much repressed short cycle, as shown by the 

 occasional production of promycelia. We know that the germ tubes 

 produced by these spores reinfect Rubus leaves. It is not known 

 whether the sporidia can cause infection. Some of the sporidia have been 

 seen to germinate. They appear normal in every way, and there seems 

 to be no reason why they should not function. 



So far as the writer knows no one has yet observed the production of 

 promycelia in cultures of the European orange-rust of Rubus. Both 

 Fischer (4) and Lindfors (8) have recently studied the manner of germi- 

 nation of the spores of this rust and have observed only germ tubes. 

 Fischer, however, has shown a branch of small diameter coming from the 

 end of one of his germ tubes. This suggests an attempt at promycelium 

 production and leads the writer to believe that if large numbers of 

 aeciospores of the European orange-rust are germinated and carefully 

 observed promycelia will be found. 



The findings of an occasional promycelium in cultures of the aeciospores 

 of Gymnoconia interstiiialis at once raised the question as to whether or 

 not such a performance is usual among the rusts. It is not possible to 



