MICHIGAN ACADEMY OF SCIENCE. 91 



FURTHER OBSERVATIOXlf^ ON THE LIFE HISTORY OF FUC- 



. CIXIA MALVACEARUM. 



J, B. DAXDEXO. 



This subject was worked over rather thorouglily by us some years 

 ago, and the result published in the 9th Report of the Michigan Acad- 

 emy of Science, 1907, but further observations on this fungus since that 

 time, seem to us to warrant a brief review with the addition of such 

 facts as have developed since then. 



As this rust has but one so-called stage — the teleuto stage — in its 

 life cycle; and as the teleuto spores germinate immediately upon reach- 

 ing maturity, the question of the wintering over has been one feature 

 most prominently of interest. It is with regard to the wintering over, 

 from year to year, that further observations led me to present this 

 brief pai>er before the Academy. 



This rust seems to be distinctly on the increase in our locality, but 

 this need give no alarm for the reason that the plants likely to be in- 

 fested l)y the fungus, are of little economic importance. In fact, if we 

 leave out of consideration the ornamental plant, Hollyhock, we might 

 say of no economic importance. The common mallow of gjirdens and 

 waste places around yards and buildings is generally considered some- 

 thing of a noxious weed, and this is the plant most commonly affected. 

 The rust, however, is likely to infest other plants of the mallow family, 

 particularly the following genera including: ^lalva, Althaea, Malvas- 

 trum, Sidalcea, Malope, and Abutilon. The following genera, though 

 growing side by side in the Botanic Garden at the College, were free 

 from the disease: Anoda, Hibiscus, Xapaea and Sida. 



A few of the species of those genera mentioned above as susceptible 

 to the disease, are considered of value as ornamental plants, especially 

 in the east, consequently the rust is of some importance from the econo- 

 mic side, and it would seem to be worth while to make some effort to- 

 ward checking it. This will be suggested in the life history here given. 



Life Historjj: The spores germinate immediately, i. e., without any 

 period of rest, producino- a promycelium on which are developed a few 

 sporidia (promycelial spores). This takes about two or three days. The 

 sporidia also germinate as soon as mature and send out an infective 

 mycelium which, under suitable conditions, enters a stomate of the 

 leaf, petiole, or stem of the host. In about seven or eight days after 

 infection, a new sorus appears, and in about ten days mature teleuto 

 spores are developed. Consequently, about two weeks is required in 

 artificial infection to complete the life cycle. This cycle of reinfection 

 goes on, — weather conditions being favorable. — the whole growing sea- 

 son. And, for the common mallow, Malva rotundifolia, this is from 

 March' to December. With us in Michigan, the common mallow is a 

 perennial and the fungus winters over in this plant. We have been 

 able to find this rust every month in the year, around old buildings 

 and in sheltered places on the south side. After a few fine sunny days. 



