UREDINIA 



321 



the aecial sorus becomes dome-shaped. As the pressure increases 

 from repeated dehmitation of the aeciospores in chains, the pe- 

 ridium is ruptured, thus Hberating the aeciospores. 



The surface markings or sculpturing of the walls of the pe- 

 ridial cells in species of Roestelia (Gvmnosporangium) has been 

 employed to distinguish species. Kern (1910) used this criterion 

 in a study involving 16 species of Roestelia. Hedgcock (1928) 

 separated the needle-inhabiting peridermiums on pines, which be- 



FiG. 122. Germination of apogamous aeciospores of Endophyllinn euphor- 



biaesylvaticae. (Adapted from Moreau.) 



long to the Genus Coleosporium, by using structural features and 

 color. 



Infection resulting from germinating aeciospores produces my- 

 celia on which urediniospores or teliospores or both are formed. 

 In a few species repeated aecium formation has been observed. 

 Secondary aeciospores have been noted, for example, in Fiiccinia 

 senecionis and in Uro7/iyces cminijigh ami amis, the latter occur- 

 ring on Jas77nmmi grandiflonim in India and appearing to consti- 

 tute the first known case of repeating aecia [Barclay (1891)]. 



Uredinia. The urediniospores are borne on the same host as 

 aeciospores in autoecious rusts but on a different species in heter- 

 oecious rusts. Urediniospores originate from mycelium, arising 

 from: (1) germination of aeciospores, (2) germination of spo- 

 ridia, or (3) germination of other urediniospores. Urediniospores 

 normally constitute the repeating spore forms, and many succes- 

 sive crops may be produced during a season. They are unicel- 

 lular and ovate to elliptical; the Mall is echinulate, and, except for 



