HARDWICKE'S SCIENCE-GOSSIP. 



197 



require, and we are putting ourselves in a h)rper- 

 critical position, if we refuse to believe what com- 

 petent observers assert, simply because we have not 

 ourselves actually seen it in all the other instances. 



^cidium ; Podisomne, Rcesteliae ; and Peridermium, 

 Coleosporium. Surely these instances are enough to 

 convince us that heteroecism does exist amongst the 

 uredines. A far more fruitful source of error has 



Fig. 136. — a, Promycelium spore of Puccinia lychntdfanun germinating upon the cuticle of Lychnis dioica. The germ-tube has 

 penetrated one of the epidermal cells, and is advancing beneath three others (July 12, 1(582 ; camera) ; b, promycelium spore 

 of Puccinia gratninis, which has penetrated an epidermal cell of Berberis z'ulgaris (24 hours) ; after De Bary ; c, spore of 

 /Ecidium berberidis germinating upon the cuticle of a young wheat plant; the germ-tube has just entered a stomatum sown 

 on leaf at 8.45 p.m., July 17 ; sketched by camera at 5.20 a.m. on the i8th ; d, two uredo spores oi Puccinia gratninis germi- 

 nating upon the cuticle of a wheat leaf; the germ-tube of the lower spore has just entered a stomatum ; in the upper spore the 

 process is more advanced ; July 18, 1882 (camera). — [Spores placed on leaf at 8.45 P.M. of July 17 ; the sketches were made 

 by the camera, the lower at 5.10 a.m., the upper at g.30 a.m. on the i8th.] 



In the course of the experiments above alluded to, 

 Pucciniae upon one host-plant, have been seen to 

 produce ^cidia upon another ; /Ecidia have been 

 seen to produce Uredines ; Uromyces has produced 



arisen from connecting an recidium upon one plant, 

 with a uredo occurring upon the same plant. For 

 example, the tecidium upon dock (^^. riimicis) has 

 been thought to be connected with the Uromyces 



