ON THESIUM 229 
fKeidia on Geranium pusillum, and possibly also on G. molle, 
G. rotundifolium; uredo- and teleutospores on Polygonum Con- 
volvulus, August and September. Uncommon. (Fig. 176.) 
The connection of the «cidium on the first-named host and the 
Puceinia on Pol. Convolwulus has been experimentally demonstrated by 
Tranzschel. It is possible that the same parasite also attacks P. dume- 
torum, P. Persicaria and others. The ecidium is not known for certain to 
have occurred in Britain. The teleuto-sori of P. Polygoni-Convolvuli are 
distinguished from those of P. Polygoni-amphibii by their compact 
pulvinate form, and by being soon uncovered by the epidermis, while the 
spores (perhaps in consequence of that) are much darker at the summit, 
and the apex, if conical, is less often oblique. According to Sydow these 
distinctions, however true they may be of the European forms of the 
species, do not avail when the extra-European forms are considered. In 
the Monographia, therefore, the two species are united, and only culture 
experiments will be able to decide the question. 
99. Puccinia Thesii Chaill. 
Geidium Thesii Desv. in Journ. de Bot. ii. 311 p.p. Cooke, Handb. 
p. 587; Micr. Fung. p. 195, pl. 3, f. 50—1. 
Puceinia Thesii Chaill. in Duby, Bot. Gall. ii. 889. Cooke, Handb. 
p. 495 ; Micr. Fung. p. 204. Plowr. Ured. p. 145. Sacc. Syll. 
vii. 602. Sydow, Monogr. i. 585. Fischer, Ured. Schweiz, p. 300, 
f. 219. 
Spermogones. Amphigenous, numerous, amongst the ecidia. 
Fig. 177. P. Thesii. Teleutospores, from a Surrey specimen. 
Aicidiospores. Aicidia amphigenous, scattered uniformly 
and rather thickly over the whole leaf-surface, seldom in roundish 
