Aug. i6, 1920 Further Data on the Orange-Rusts of Rubus 509 



cultures of aeciospores kept at about 10° for a week or longer. It 

 must be understood, however, that they are not produced very abun- 

 dantly even under favorable conditions. Sometimes 1,000 germinated 

 spores may be observed without the finding of a single promycelium, 

 but usually several promycelia will be found for each 1,000 spores 

 observed if the cultures are more than 4 days old. In some cultures 

 they occur more abundantly. 



It is interesting to note that most of the promycelia developing in 

 cultures of the aeciospores of the long-cycled rust are abnormal, though 

 normal ones are also present. Many of the abnormal promycelia pro- 

 duce one or more normal sporidia, and there can be no doubt regarding 

 their true nature. The abnormal promycelia and their tardy appearance 

 in the cultures seem to the writer to suggest that nuclear fusions and 

 the subsequent reduction divisions are steps accomplished with diffi- 

 culty in these spores. It would be highly interesting to study these 

 phenomena cytologically, but the relatively small number of promycelial 

 germinations makes such a task rather difficult. 



From a study of many abnormal promycelia the writer has come to 

 recognize certain structures as indicating an attempt at the production 

 of sporidia. Some of these are cross walls, branches, especially those 

 having a diameter less than that of the germ tube, and sporidia-like 

 processes borne on structures that show more or less resemblance to 

 sterigmata. In cultures of the aeciospores of the long-cycled orange- 

 rust it is possible to find all gradations between normal promycelia and 

 germ tubes that can hardly be recognized as promycelia at all. In order 

 to show some of the stages between these two extremes a few drawings 

 have been made of abnormal promycelia. 



Figure 53 of Plate 94 shows a tube with two rather typical sporidia 

 borne on typical sterigmata. No cross walls occur in this tube. Figure 

 49 shows a branched germ tube. A cross wall occurs just below the 

 branch. No sporidia are borne on this tube, but there can be little 

 doubt that this is an attempt at promycelium production. Figure 51 

 shows a germ tube with one cross wall and forked branches. One of 

 these branches has produced a rather long club-shaped tube, while the 

 other has developed into a sterigma-like process bearing a typical spo- 

 ridium. A tube with one cross wall and several branches of small 

 diameter is shown in figure 50. One of these branches is pointed like 

 a sterigma and bears a spore that resembles a sporidium. Figure 45 

 represents a tube having one cross wall and several short branches. One 

 of these branches is considerably enlarged toward its distal end and 

 presents curves that suggest those of the normal sporidium. A short 

 tube is sho%vTi in figure 47. This tube has one short branch which bears 

 a sporelike body having curves that closely resemble those of a sporidium. 

 The curves of the upper end of this body are especially like those of the 



