O I II ni an Eu-form 



RUST FUNGI 189 



have only one cell. These different kinds of spores, representing stages 

 in the life histories of the different genera and species of rusts are 

 designated, as follows: O = pycnium; I = aecium; II = uredinium; 

 in = tehum. The determination of the presence or absence of these 

 spores in the various life histories has been made for a large number of 

 rusts, and we are now in a position to tabulate the results of this study 

 and to give names to the different forms of rust life cycles which have 

 been found. We call a fungus possessing: 



Auteu-form, if all four kinds are found on one plant 



(Ex. Puccina Asparagi on Asparagus officinalis). 

 Hetereu-form, if O, I occur on one species and II, III 

 on another (Ex. Puccinia graminis is on wheat and 

 barberry). 

 O I III an opsis-form (Ex. Gymnosporangium Juniperi-virginiantE, O, I on 



apple, and III on red cedar). 

 O II III a Brachy-fonn (Ex. Puccinia suaseolcns on Canada thistle). 

 [O] III a Micro-form pycnia (spermogones) sometimes absent (Ex. Puc- 



cinia riiiis on currant). 



A Lepto-form is one, of whatever kind, in which the teliospores 

 grow as soon as mature without any period of rest, as Fuccinm ttialva- 

 cearum on hollyhock. W. B. Grove in his "British Rust Fungi," 

 page 40, gives a diagram which represents aU of the possible life cycles 

 of the different forms of rust fungi. It is reproduced here (Fig. 65). 



As a fungus which shows a complete life history passed on two dis- 

 tinct host plants, we will take the black rust of cereals, Puccinia 

 graminis (Fig. 64), first carefully studied by the German botanist, 

 Anton de Bary, in 1864-65. It infests all the common cereals, wheat, 

 rye, barley and oats, also many grasses. It appears on the wheat 

 plant, when the host is about ready to produce its spikes of flowers. It 

 appears on the leaves and culms of the wheat plant, as orange-red 

 lines, which represent cracks in the epidermis of the host exposir^ the 

 sori, or uredinia fiUed with rust-red spores, urediniospores. These 

 summer spores are yellowish and their surface spinvQose with four equa- 

 torial germ pores. These urediniospores ma\- follow each other on 

 several crops during the early summer. This summer stage is succeeded 

 by the autumn stage in which the sori become fiUed with stalked, 

 two-celled, dark-colored spores with thick walls. The common name 

 of this stage is "black rust." Wintering in the open these two-celled 

 teliospores germinate. Each of the two ceUs may sprout out a pro- 

 mycelium, or only one may do so. This basidium (promycelium) is 



