146 PLANT MORPHOLOGY 



if all stages are passed on the same host, or on closely related hosts, it is 

 autoecious. Gymnosporangium juniperi-virginianae, a heteroecious rust, 

 has no uredospores. It develops the telial stage on the red cedar {Junip- 

 erus virginiana), or related species, and the aecial-spermogonial stage on 

 the apple, pear, and quince (Pyrus). A heteroecious rust of great eco- 

 nomic importance is Cronartium ribicola, the white pine blister rust. Its 

 uredospore-teliospore stage is passed on various species of currants and 

 gooseberries (Ribes), its aecial-spermogonial stage on the white pine 

 {Pinus strobus) and related species. The damage to white pines has 

 been so great that it has resulted in their virtual extinction in many parts 

 of the country. Puccinia asparagi is an autoecious rust, producing 

 uredospores, tehospores, aeciospores, and spermatia on the asparagus. 

 Pxiccinia malvacearuvi, another autoecious rust, has a very short life cycle, 

 producing only teliospores on the hollyhock and other Malvaceae. 



3. Auriculariales 



The Auriculariales are the ear fungi, an order of about 15 genera and 

 over 100 species. They are chiefly saprophytes growing on bark and 

 decaying wood. The representative genus is Auricularia. The myce- 

 lium produces brightly colored, gelatinous, ear-shaped bodies, each being 

 a basidiocarp. When dry, the basidiocarps become wrinkled and hairy. 

 The inner surface is lined with a hymenium consisting of basidia inter- 

 mixed with paraphyses. As in the Uredinales, the basidia are four-celled 

 and have sterigmata. Each basidium produces four basidiospores. This 

 order may be regarded as transitional between the lower and higher 

 Basidiomycetes. 



4. Tremellales 



The Tremellales, or trembhng fungi, are somewhat similar to the 

 Auriculariales. They include 18 genera and nearly 100 species, the best- 

 known genus being Tremella. The mycelium lives in decaying wood and 

 bark, producing gelatinous basidiocarps. These are indefinite in form 

 and more or less wavy or folded. The hymenium occurs on the upper 

 surface. The basidia are characteristic, being longitudinally divided into 

 four cells instead of transversely divided. Each basidium bears four 

 basidiospores on long sterigmata. 



5. Exobasidiales 



The Exobasidiales are internal parasites attacking particularly mem- 

 bers of the Ericaceae, such as blueberries, cranberries, huckleberries, 

 azaleas, etc. There are about 30 species, nearly all belonging to the 

 genus Exobasidium. Galls composed of mycelium and host tissue are 

 produced on stem tips, leaves, and floral organs. The basidia are formed 

 under the epidermis and, when they break through, cover the host with a 



