92 TWELFTH REPORT. 



sori develoj) fi-oni the doi-inant iiiyoeliTiin in the 'stems and petioles. It 

 winters over with the common mallow, and if the eommoii mallow be 

 eradicated, it is our opinion that the disease wonld be practically under 

 control. 



Some authors assert that the teleuto spores winter over and thus carry 

 the disease from year to year. This is clearly not the case here. The 

 teleuto spores germinate as soon as mature, therefore it would be jiracti- 

 cally impossible to keep them dormant during- the winter. If they did 

 germinate, the sporidia would at once die. Moreover the first appearance 

 in earliest spring is on the stems and petioles, the youngest leaves being- 

 free. This shows that the infection is already in the plant remaining 

 dormant during frost and developing during fine weather. 



The teleuto spores germinate in the sorus, — producing a grayish ap- 

 pearance while the ungerminated are of a clear amber-brown color. 

 The Promycelium grows in a direction parallel with that of the i>edicil 

 of the teleuto spore, so that they project out in all directions from the 

 sorus, and it is our opinion that these sporidia are the means of in- 

 fection, that is to say, they and not the teleuto spores, are carried from 

 place to place. This may be inferred from the fact that the teleuto si)ores 

 germinate "in s/fw." We infer, also, that infection can not take place 

 at very great distances, because the sporidia are delicate bodies and will 

 not stand drv air for anv great length of time. This feature is something 

 which in itself would jirevent wide spread infection. It does spread, no 

 doubt, but slowly. Seedling mallows out in garden or orchard are usu- 

 ally not atfected at all, until very late in the season. The rust can 

 always be found where the mallow grows in uncultivated ground peren- 

 nially. 



To combat the disease, eradicate all the old mallows in the fall. 



In my paper before this Academy in 1907, it was stated that the 

 fungus wintered over in the mallow. ^Ve are now more firmly con- 

 vinced than ever of this. In this connection it might be worth while 

 to say that one or two facts were brought out during the discussion fol- 

 lowing the paper, namely that the rust wintered over on the Hollyhocks 

 around Ann Arbor, and that in the neighborhood of St. Louis, Mo., it 

 was common on Hihisciis while Ahufilon appeared to be free from the 

 rust. The writer assumes no responsibility for these statements, al- 

 though the authority is doubtless reliable. 



East Lansing, Mich., April 1010. 



