CRYPTOGAMS 367 



wind to the haulms of grasses, upon which alone they can germinate. The 

 mycelium thus developed produces, particularly on the leaf - sheaths, primarily 

 uredospores (Fig. 288, 5). They are unicellular, studded with warty protuberances, 

 and provided with four equatorially disposed germ-pores. In consequence, the 

 reddish-yellow fat globules contained in the protoplasm of the spores form red 

 markings (formerly termed Uredo linearis) on the epidermis of the host-plant. 

 The uredospores are capable of germinating at once on the same or other cereals, 

 and thus the rust disease is quickly spread. Towards the end of the summer 

 the same mycelium produces the black, thick- walled teleutospores, which in this 

 species are always double, being united in pairs. Each teleutospore is provided 

 with one germ -pore, and on germination in the succeeding year the cycle is 

 begun afresh. 



The mycelium of the Uredo form may hibernate in winter wheat, and thus the 

 rust may appear in the spring without the previous formation of basidiospores or of 

 secidia. 



Other Rust Fungi, like Puccinia graminis, common on Gramiiwae, and having 

 a similar development, are P. Rubigovera (= P. straminis), with the aecidium 

 form, JEcidium Asperifolium on the Boragineae, and P. coronata, with the corre- 

 sponding form, JEcidium Rhamni, on Rhamnus. 



All Uredineae do not exhibit so complicated a course of development as Puccinia 

 graminis. Certain species produce only basidia from germinating teleutospores 

 (e.g. Puccinia Malvacearum, now very common on the Malvaceae, but originally 

 introduced from Chili). Puccinia bistortac on Polygonum bistorta gives rise, in addi- 

 tion to teleutospores, only to uredospores which are developed on the same host. 

 Puccinia fusca produces pycnidia and aecidia (Fig. 287), and afterwards teleuto- 

 spores on the leaves of Anemone nemorosa, but no uredospores. In the develop- 

 ment of various forms of chlamydospores, either a different degree of advancement 

 is thus manifested in the different groups, or by » process of degeneration one or 

 other spore -form has been lost. There are, moreover, species whose reproduc- 

 tion is effected chiefly or exclusively by uredospores or by ascidia. In such cases 

 it must be inferred that as the result of the environment the production of teleuto- 

 spores has been almost wholly or altogether suppressed. For example, it is stated 

 that in the tropical climate of Ecuador, Uromyces Fabae on Vicia Faba multiplies 

 solely by means of uredospores. 



In the case of the hetercecious species, it is only possible to demonstrate the 

 connection between the different spore-forms by means of culture experiments. So 

 long as the relation of the different forms was not known, it was customary to 

 designate each by a special generic name ; the Uredo forms as Uredo ; the iEcidia, 

 according to their structure, as JEcidium, Roestelia, Peridermium, etc. The 

 generic name is now determined by that of the teleutospores, as they exhibit the 

 most characteristic distinctions. 



Many of the Uredineae are injurious parasites, e.g. Gymnosporangium Sabinae, 

 whose teleutospores develop on Juniperus Sabina, while the aecidia and pycnidia 

 occur on Pirus Communis. The secidium produces the so-called lattice rust on the 

 leaves of the pear tree, and has been termed Roestelia eancellata. The Rust Fungus 

 found on the needles and bark of various species of pines, and formerly known as 

 Peridermium, is due to sac-shaped aacidia, which belong either to the genus Coleo- 

 srtorium, whose uredo- and teleuto-forms occur on the Compositae and RMnanthaceae, 

 or to the genus Cronartium, with uredo- and teleuto-forms on Vincetoxium and 

 Ribes. Especially destructive to the tropical coffee culture is Eemileia vastatrix, 

 which produces both its uredospores and teleutospores on the leaves of coffee plants. 



