70 



NINTH REPORT. 



certain patches of mallows which were, to all appearances, free from the rust. 

 If the teleutospores had survived the winter, it was thought that infection 

 of these fresh young mallows must result. The infected litter did not seem 

 to produce any result whatever. The wintering over is accomplished in 

 aiiother way. 



On examining mallows very early, — about April 10 — in 1906 and 1907, 

 well-developed teleutosori were found on leaves and petioles. These- mal- 

 lows had wintered over as perennials in the shelter of the grass alongside of 

 a hedge, and also alongside some of the college buildings, so that practically 

 as soon as the mallow commenced to grow — and, that was almost as soon as 

 the snow disappeared — the teleutosori were plainh' seen. The spores from 

 these sori germinated readily when taken into the laboratory and placed 

 under favorable conditions there. It seemed apparent then that the fungus 

 wintered in the living portions of such affected mallows as withstood the 

 winter. iStill it seemed curious that the parasite being able to withstand 

 the winter in such a way as to have such an early start in spring, should nc^t 

 become so abundant during summer as it does in the fall. On examining, 

 from time to time, those mallows which were infested in April, it was found 

 that the fungus spreads only very sparingly over the other leaves of the same 



plants, or over leaves of neighboring plants; and in July and August it seemed 

 almost to disappear, then to recur about September 1st, on the hollyhock, 

 and about October 1st, on the mallow and other species of- the same family. 

 The reason for this slow development of the fungus in simimer, and its con- 

 secpient rarity at this time, is not very apparent, yet from the fact that it 

 does better in cool weather it may be that temperature and moisture are im- 

 portant factors; but these can scarcely be the only factors. It may be that 

 an enfeebled condition of the host plant is also no unimportant factor. 



This rust was found in the Botanic Garden here on species of the following 

 genera of the mallow family: Malva, Althaea, Alalvastrum, Sidalcea, Malope, 

 Abutilon, but not on Hibiscus, Sida, Napaea, Anoda, though in the gardens 

 all ten genera were growing practically side by side. With those plants 

 upon which the rust was found, it was very abundant, especial!}^ in the fall of 

 the year 1905. 



