The production of a promycelium by the aecidiospores of Caeoma 
nitens Burrill 
Otto KUNKEL 
INTRODUCTION 
Except in the genus Endophyllum, so far as known, the aecidio- 
spores of the rusts give rise to sporophytic mycelium. Its sporo- 
phytic nature is shown by the fact that each cell contains two 
nuclei that have been produced by successive conjugate divisions 
of the two nuclei in the aecidiospore. The aecidiospores of some 
of the species of Endophyllum, however, produce a promycelium. 
Its cells are uninucleate and belong, therefore, to the gameto- 
phytic generation. This fact has been well established through 
the work of Tulasne (10), Sappin-Trouffy (8), Maire (5) and 
others. Hoffmann has shown that nuclear fusion occurs in the 
aecidiospores and that this fusion nucleus divides to form the 
nuclei of the sporidia. This interesting form has received con- 
siderable attention in recent years, because its life history offers 
suggestions regarding evolution in the rusts. 
While engaged in a study of the effects of media on the germina- 
tion of various spores I was surprised to find that the aecidiospores 
of Caeoma nitens taken from leaves of Rubus frondosus Bigel. on 
germination produce a promycelium in much the same way as 
do the aecidiospores of Endophyllum Sempervivi Lév. My first 
suspicion that this might be due to the influence of the medium 
upon which the spores had been placed proved groundless, for 
further tests showed that they germinate in exactly the same 
way when placed in distilled water or in tap water. The 
production of a promycelium by these aecidiospores seems to 
have escaped the observation of the numerous students of this 
common and widely distributed rust. 
Galloway (6) figured them germinating in water and 
shows that the germ tube becomes more or less septate. 
He did not, however, observe the production of sporidia 
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