RUST FUNGI 191 



amphispores, as they have been termed by some, but in conversation 

 with Arthur he insisted that the perennating spores are typical uredinio- 

 spores, so that the postulation of a perennial mycelium, or a hibernating 

 fungous protoplasm in the cells of the grain (mycoplasm) is unneces- 

 sary. Eriksson has proved that in Sweden six forms of Puccinia 

 graminis may be distinguished; which he enumerates as follows: 



A. Not distinctly fixed (occasionally going over to other forms of 

 grass): (i) f. sp. tritici on wheat (seldom on rye, barley and oats). 



B. Distinctly fixed (firmly confined to the indicated species): (2) 

 f. sp. secalis on rye, barley and on couchgrass, Agropyron repens, Ely- 

 mus arenarius, Bromus secaUnus and others; (3) f. sp. avenae on oats 

 arid on Avena elatior, Dactylis glomerata^ Alopecurus pratensis, Milium 

 efusuni and others; (4) f. sp. poae on Poa compressa and P. pratensis; 

 (5) f. sp. airae on Aira ccespitosa and ^4. hottnica; (6) f. sp. agrostis on 

 Agrostis canena and A. stolomfera. An oat plant infected with this rust 

 can in its turn infect wheat, rye, barley and so forth. The black rust 

 of cereals is the classic example of an heteroecious rust. 



The asparagus rust, Puccinia asparagi, may be used to illustrate the 

 life history of an autoecious species. All the spore forms are pro- 

 duced on stems and twigs. The aecia appear in long, light green cush- 

 ion-like areas, which are short cylindric with a white peridium. The 

 aeciospores are orange-colored and the wall is hyaline. The pycnia 

 appear in yellow clusters followed by the aeciospores in early sum- 

 mer. The uredinium is filled with yellowish-brown, thick-walled uredi- 

 niospores w'ith three or four germ pores. The black rust stage (telium) 

 appears later in the season, when the two-celled stalked teliospores push 

 out from beneath. The whole life cycle is passed on the asparagus 

 plant. 



Cytology of the Rusts. — According to the earlier researches of 

 V. H. Blackman (1904), A. H. Christman (1905), O. H. Blackman and 

 Miss H. C. Fraser (1906), Edgar W. Olive (i9o8),Kurssanow (1910) and 

 Dittschlag (191 6), supplemented by the research of other botanists, a 

 flood of light has been thrown on the nuclear behavior in the rusts, and 

 accordingly on their sexuality, or non-sexuality. Blackman discovered 

 in Phragniidium violaceum (Fig. 66), that in the formation of the 

 aecidium, there was a fusion of two cells by which the nucleus of one 

 passed over into the adjoining cell. In the formation of spores the 

 paired nuclei of the fusion cell divide side by side and simultaneously 

 (conjugate division) so that we find that the basal cell, the aecio- 



