ON PRUNUS 209 



Teleutospores. Sori similar but blackish-brown ; spores 

 ellipsoid to oblong, composed of two globose cells which readily 

 separate (or lower cell often narrower, paler and imperfect), not 

 thickened above, densely and coarsely verrucose, brown, 30 — 

 45 x 18 — 25 fi ; pedicels hyaline, very short, deciduous, spring- 

 ing in clusters of about 10 — 20 from a common base. 



iEcidia on Anemone coronaria, A. nemorosa, April and May; 

 uredo- and teleutospores on Primus domestica, P. insititia, 

 P. spinosa, also on cultivated species and varieties of Primus 

 and its allies, August — October. Common in certain districts. 

 (Figs. 155, 156.) 



The discovery of the hetercecism of this parasite is comparatively 

 recent. Tranzschel first showed (in 1904) that it was hetercecious, using 

 Anemone coronaria and Amygdalus communis as the alternate hosts. 

 F. T. Brooks, at Cambridge in 1911, laid fresh secidiospores from the same 

 species of Anemone on both sides of certain leaves of a "Victoria" Plum, 

 leaving others uninoculated. The plant was enclosed by a bell-jar, 

 and three weeks later twenty-three of the inoculated leaves were found to 

 bear on their under-surface uredo-sori of P. Pruni-spinosae, while the 

 control leaves showed no signs of the rust (New Phytologist, x. 207). 

 Arthur, in the United States, proved a similar fact, but in that case the 

 host of the alternate phase was Hepatica acutiloba, a very close ally 

 of Anemone. The a;cidium is also reported on other species of Hepatica, 

 Anemone ranunculoides and other species of Anemone, Eranthis hiemalis, 

 and various species of Thalictrum. 



Scribner (Report of the Dept. Agric. U.S.A. 1887) describes the Puccinia 

 as found on Cherry, Apricot, and Peach : it is recorded by McAlpine 

 on leaves, fruit and stems of Peach and Nectarine, and leaves and fruit of 

 Almond and Apricot. 



Trichobasis llhamni of Cooke (Seem. Journ. Bot. ii. 344, iv. 104) on 

 " Ithamnus catharttcus," which was afterwards referred by him to this species 

 (Handb. p. 508), is probably an error due to a mistake in the identification 

 of the host. He states that the Puccinia on the same leaf was absolutely 

 identical with P. pruni-spinosae., and omits the reference in the fourth 

 edition of " Microscopic Fungi." No one else has found such a Puccinia 

 on Rhamnus. The leaf in " Micr. Fung." ed. i. 210, is no doubt a Primus 

 leaf. 



The mycelium of the pecidial stage is perennial ; it penetrates in spring 

 into the growing shoots which become deformed, the affected leaves are 

 narrower and paler, and the flowers are usually imperfect or altogether 

 wanting. These plants it is which cause fresh infections of the Plum-trees 



G. u. 14 



