219 



Continuous Rust Propagation Without Sexual 

 Reproduction. 



C. A. Ludwig. 



With the demonstration of heteroecism in the rusts, the teliospore came 

 to be looked upon as primarily a resting spore, for heteroecism was first 

 proved for the black rust of grasses, in which the teliospore is a true rest- 

 ing spore. It was therefore believed by implication, indeed often stated, 

 that the teliospore is the means of carrying rust fungi over unfavorable 

 weather conditions and is especially equipped structurally for that func- 

 tion. The other spore forms and the mycelium, except in the comparatively 

 rare cases of a mycelium diffused through and perennial in the tissues of 

 the host, were not supposed to be able to survive such adverse conditions. 

 Later when modern cytological methods were applied to the rusts, it was 

 found, as some leading uredinologists had already suspected in a rather 

 vague way, that the essential feature of the teliospore is that, it is the 

 structure in which is begun the series of nuclear phenomena which close 

 'the sporophytic stage and precede the gametophytic stage with its resulting 

 sexual fusions. With this latter idea goes the rather common belief that 

 no type of life, plant or animal, except perhaps the very lowest, can long 

 maintain a high degree of vigor without at least occasional sexual fusions. 

 It is this idea that has given rise to the belief held in many places that if 

 all the barberry bushes could be destroyed, the black rust of cereals would 

 not be able to maintain itself more than a few years. Thus we have super- 

 imposed one upon tbe other in the minds of many men these two ideas : 

 (1) that tbe teliospore is necessary to tbe continued existence of the rust 

 because it is the means of passing the winter or other unfavorable season, 

 and (2) that it is necessary to the vigor of the fungus because it is the 

 structure in which are initiated those changes which culminate in sexual 

 fusions and without which such fusions would not take place. The con- 

 tinued prevalence early in the season of tbe grain rusts at great distances 

 from any possible seeia of the species, however, led some investigators to 

 doubt tbe validity of the beliefs just recorded. In consequence, a number 



