PUCCIN1A MALVACEARUM 41) 



way (Fig. 29). The accumulated basidia and spores give a 

 greyish tinge to the red-brown sorus. These spores can cause 

 fresh infection and so the disease spreads rapidly. It is most 

 active about the end of summer, and has often been the cause 

 of a serious epidemic on the more susceptible kinds of Holly- 

 hock. The sori are found on every green part of the plant, 

 stems, leaves, petioles, bracts, sepals, carpels and fruits, and are 

 even reported on the petals. There are no uredospores. 



The chief biological interest of this fungus concerns the 

 way in which it passes the winter, a point about which there 

 has been much dispute. There are two possibilities, (1) by 

 perennial mycelium, (2) by over-wintering teleutospores. The 

 first has been strongly advocated, and it is very likely (though 

 one can hardly say it has been proved) that the mycelium does 

 winter in the young leaf-rudiments that are formed on shoots 

 at the base of last year's stems. Freshly formed sori have also 

 been found on the cotyledons of seedlings which grow up in 

 late autumn round the parent plants and which in certain 

 cases can survive the dead season. But there seems to be 

 absolutely no justification for the claim that the mycelium 

 winters in the embryo of the seed. The disease can undoubt- 

 edly be carried with the seed, in sori either on the bracts 

 (portions of which are often mixed with the "seeds," i.e. fruits) 

 or on the outside of the carpels themselves. 



Eriksson has lately {Ueber den Malvenrost, 1911) published 

 a theory, similar to his well-known theory about the Rust of 

 Corn, and standing or falling with it : he says that P. Malvace- 

 arum perennates in the form of " mycoplasm " in the cells of 

 the autumn buds at the base of the shoots, as well as in the 

 embryos of the seeds of the infected plants. With these he 

 says it grows up in an imperceptible form, mingled with the 

 protoplasm of the host, permeating the newly-formed leaves 

 and at last suddenly breaking out in the form of pustules of 

 primary teleutospores, which afterwards spread in the acknow- 

 ledged way. He explains the presence of this mycoplasm by 

 stating that certain teleutospores of the previous autumn 

 germinated by sending out " germ-tubes " which cut off " end- 

 conidia." (This mode of germination of the late-formed spores 

 o. u. 4 



