22 INVESTIGATIONS OF RUSTS. 



itself is well known to have extremely narrow leaves. Moreover, the 

 spores were not germinated when applied, and, being from dried speci- 

 mens, the incubation period would naturally be long. Seedlings of 

 S. cryptandri were not at the time available. On March 16 a second 

 water-drop culture was made from this dried material, resulting in the 

 germination of a few spores. 



Teleutospores from herbarium specimens have often been germi- 

 nated, but the writer knows of no other instance of the germination 

 of dried uredospores, such spores being able also to infect a different 

 host. These observations and experiments indicate that we have 

 here a second step in the perfection of the uredo stage as a means of 

 propagating the species. The rirst step, the attainment of sufficien 

 hardiness to continue alive in the green plant over winter, has just 

 been discussed. Even in this case the uredo, although quite active, 

 at least displaces the resting spore, and in a measure performs its part. 

 But as the perennial host becomes more like an annual and the plant 

 dies nearly or quite to the ground, as in this particular case of the 

 Sporobolus (which is quite different in this respect from the evergreen 

 Poa pratensis, for example), necessarily, in the absence of teleuto- 

 spores. the uredospore must be able to infect after a dormant period. 

 The uredospore therefore becomes now practically a resting spore, 

 but retains the appearance and manner of germination of the summer 

 spore. Such a modification in form or function of any stage of a 

 species to correspond with an unusual change of condition of climate 

 or of the host may be considered as an emergency adaptation. 



It is easily understood how the change of conditions may be so 

 severe as to necessitate still further modification of structure as well 

 as function, simply as a means of protection. Such a development 

 seems to have been actually reached in the species next discussed, 

 which has resulted in the production of a distinct spore form, special- 

 ized from the uredo, leaving still, however, a true uredo stage for 

 summer propagation. 



PuCCIXIA VEXAXS FaRL. 



There are probably no other species in all the Uredinea? more inter- 

 esting than this one, and certainly none that has been more perplex- 

 ing. In this species there are three distinct spore forms aside from any 

 aecidium or spermogonium that may possibly exist — true uredo and 

 teleuto stages, and a peculiar one-celled form different from either of 

 these. (PI. II. figs. 2-9.) The species was at first made all the more 

 puzzling by the rarity of the true uredo stage, which was not known 

 to exist, or at least not reported, until 1S90, when Dr. H. J. Webber, 

 in the Catalogue of the Flora of Nebraska, reported its occurrence in 

 that State. In certain seasons and localities the teleuto stage also is 

 almost or entirely lacking. 



