MAMMOTH CLOVER RUST^ 



W. H. DAVIS 



Before the work of Liro, there was thought to be but one clover 

 rust. He proved the rust on white clover to be autoecious and it 

 was classified as Uromyccs trifolii-repentis (Cast) Liro. It has 

 been shown that the rust on red clover is also autoecious, having all 

 four stages on red clover, and it is generally classified as Uromyces 

 trifolii (Hedw. f.) Liro. The rust on alsike clover is autoecious, 

 having all the stages, and was classified as Uromyccs hybridi, Davis, 

 in Vol. XXIV, Iowa Academy of Science, 1917. 



The disposition of the rust on mammoth clover is not clear. 

 Morphological examinations of the spores have caused taxonomists 

 to assign this rust to the species on red clover or U. trifolii (Hedw. 

 f.) Liro, but no inoculations have been made to prove this sup- 

 position. The teliospores and urediniospores of the rusts on the 

 red and mammoth clovers are similar in size and in number of germ 

 pores together with other structures. An aecial stage has not been 

 reported on mammoth clover ; it is taken for granted that only the 

 uredinial and telial stages of red clover rust are found on the mam- 

 moth by vising the mammoth as another host. Thus three important 

 questions arise : 



1. Is the rust on mammoth clover the same as that found on red 

 clover? 



2. Is an aecial stage found on mammoth clover?^ 



3. Is this an autoecious or heteroecious rust? 



With these questions in mind, the solution of this problem was 

 started in the fall of 1918. Herbarium specimens of rusted clover 

 plants of different species were collected. The winter being very 

 open, plants could be dug from out of doors and repotted at va- 

 rious times. The plants were placed in the greenhouse and the 

 rust harbored all winter. 



The (Tcial stage, aciosporcs and pycnia. — Plants of mammoth 

 clover were repotted from out of doors on December 9, 1918. 



IThe usage of the common and species names are as follows : White clover, 

 Trifolium repentis L. ; Red Clover, Trifolium pratense L. ; Alsike, Trifolmm hy- 

 hridum L. ; Mammoth — a species of red clover, generally classified as rrifoliuin 

 medium L. Leaflets hairy, entire, spotless, notched at tip. Stipules mostly 

 smooth. Stems larger and taller than red clover. 



