ORDER UREDINALES (tHE RUSTS) 405 



into the epidermal cells of the stem, there forming clusters of two to four 

 closely united teliospores which send forth their promycelium almost im- 

 mediately, through the epidermal cell walls. In Cronartium the gameto- 

 phytic (monocaryon) mycelium is perennial in the twigs and cortex of 

 older limbs of pine (Pinus), often causing the formation of galls which may 

 attain great size and age, up to the size of a human head in C. quercuum 

 (Berk.) Miyabe. The uredia are small, with a peridium. The teha are 

 rows of teliospores united laterally into a waxy column 6 to 8 rows in 

 thickness and bursting through the epidermis and projecting several milli- 

 meters. These columns continue to grow at the base for some time. Each 

 of the hundreds of teliospores of the column germinates immediately by a 

 curved promycelium producing almost spherical sporidia. The dicaryon 

 stage is found in various Flowering Plants (Anthophyta), apparently only 

 in Dicotyledoneae. In Chrysomyxa the tehospores are in separate chains 

 of three or more spores each which arise at the base of the sorus. The 

 urediospores are also in chains. The sporophytic phase occurs in the 

 Family Ericaceae in the wider sense and in a few other families. Coleo- 

 sporium and Melampsora both produce subcuticular or subepidermal 

 crusts one cell thick of laterally united teliospores. In the former the 

 urediospores are produced in short chains and the promycelium is "in- 

 ternal." In the latter the urediospores are single and the promycelium is of 

 typical structure. Coleosporium solidaginis (Schw.) Thiim., on Aster spp. 

 and Solidago spp. is abundant even in those parts of the United States 

 where the aecial hosts (species of Pinus) are not found. It is apparently 

 able to maintain itself by overwintering mycelium or urediospores. Me- 

 lampsora medusae Thiim. causes the spotting of leaves of various species 

 of poplars iPopulus) with the dark-colored telial sori, these being pre- 

 ceded by the small powdery yellow uredial sori. The aecial host is the 

 larch {Larix sp.) on whose young needles the almost white aecia appear. 

 Most of the species of this genus have their aecia on Pinaceae, but M. 

 lini (Pers.) Lev., on flax (Linum usitatissimum L.) is autoecious as is M. 

 euphorUae (Schub.) Cast. In M. rihesii-purpureae Kleb., the tehal stage 

 is on Salix but the aecial stage occurs on species of Ribes and Grossularia, 

 while three other species with Salix as their telial host have as their aecial 

 hosts respectively Saxifragaceae, and Larix and Ahies in the Pinaceae. 

 One microcychc species M. farlowii (Arth.) J. J. Davis, occurs in the 

 United States on Tsnga canadensis (L.) Carr. of the Pinaceae. (Figs. 134, 



135.) 



Family Pucctniaceae. Teliospores usually stalked, simple or com- 

 pound, sometimes without stalks and produced successively as simple or 



Fig. 135. Subclass Teliosporeae, Order Uredinales, Family Melampsoraceae, (A) 

 Cronartium flaccidum (A. & S.) Wint. ; teliospore column growing up through uredium. 

 (B) Coleosporium sonchi-arvensis (Pers.) L6v.; vertical section through telium. (After 

 Sappin-Trouffy: Le Botaniste, 5:59-244.) 



