(396) 



on the angiosperms function as resting spores, serving to carry 

 the fungus through the winter, germinate in the spring and pro- 

 duce the aecial phase on the gymnosperms, where it remains until 

 summer when it passes back to the angiosperm host again. In 

 Gymnosporangium the teliospores are on the gymnosperms. They 

 are active spores germinating upon maturity, producing the alter- 

 nate phase on the angiosperm host, where it remains about the 

 same length of time that the aecial phase of the other genera re- 

 mained on the gymnosperm host, i. e., about one quarter of the 

 year, passing back in the late summer to the gymnosperm host. 

 Here mycelium is produced which functions as a resting stage 

 during the winter or possibly during two winters in some species. 

 The foregoing diagrams may serve to illustrate these points. 



Nuclear History 



Although the nuclear phenomena in the rusts have been receiving 

 considerable attention from cytologists in recent years, not a 

 great deal of work has been done with the members of this group. 

 Sappin-Trouffy (1896) and Blackman (1904) have used some of 

 the species, especially G. clavariaeforme, in tracing certain of the 

 nuclear changes. While our knowledge is still incomplete, it 

 may, nevertheless, be well to briefly call attention to a few of 

 the more essential points which have been demonstrated. 



The basidiospores (sporidia) are uninucleated and give rise to a 

 uninucleated mycelium which bears pycniospores, also uninu- 

 cleated. At the base of the aecia, which soon begin to be formed 

 from the same uninucleated mycelium which produced the pycnia, 

 conjugation or cell-fusion takes place. This results in a binu- 

 cleate condition of the aeciospores, owing to the fact that the nuclei 

 from the two conjugating cells do not fuse. These nuclei divide 

 conjugately in the mycelium originating from the aeciospores and 

 remain separate until the teliospores are produced, where fusion 

 is usually effected by the time the teliospores are mature. 



It is to be noted that the method of conjugation in the type of 

 aecium possessed by the species of Gymnosporangium has not 

 yet been made clear. The work of Richards (1896)^ Olive (1908), 

 and others indicates that in an aecium of this type the "fusion 

 cell" does not at once function as a basal cell at the bottom of 

 each spore-column, as it does in some types of aecia, but that large 

 multinucleated cells first develop after conjugation and that the 



