VIOLENT DISCHARGE OF AECIDIOSPORES 553 



other slides, moistened on their under surfaces, at various distances 

 above the aecidia. On the next day he found that the under sides 

 of all the slides which had been suspended 10-15 mm. above the 

 aecidia were densely covered with aecidiospores. On the under 

 sides of slides susjDended at greater and greater heights than 

 15 mm. the aecidiospores became fewer and fewer, until there were 

 none at all. It was further observed that, where spore-discharge 

 had not been hindered by suspended slides, the aecidiospores had 

 settled on the leaf for some distance all round the outside of each 

 aecidium. By the third day after the experiment had been set up 

 the aecidia had freed themselves from spores almost down to the 

 base of each cup. 



When Zalewski tilted the Euphorbia leaves to an angle with the 

 vertical, he found that the aecidiospores were discharged to a hori- 

 zontal distance of 15-20 mm. 



Zalewski successfully repeated the experiments made on the 

 aecidia of Uromyces Pisi with aecidia of other species which he 

 named as follows : 



Pucciiiia straminis on Lycojhsis arvensis, 



Aecidiurn Symphyii on Symphytum officinale, 



Puccijiia Calysfegiae on Calysiegia sepium, 



Puccinia coronata on Rhamnus leaves. 



From the above series of experiments Zalewski came to the 

 conclusion that, in the Uredineae, the aecidiospores of each aecidio- 

 spore-chain are violently and successively discharged from the 

 aecidium, the oldest outermost spores being discharged first. 



Zalewski also observed that there was greater violence of dis- 

 charge from aecidia developed on thick leaves than on thin. Thus 

 the aecidia on the thick leaves of the Euphorbia, the Lycopsis, and 

 the Symphytum discharged their spores to a greater distance than 

 the aecidia on the relatively thin leaves of the Calystegia (Con- 

 volvulus) and the Rhamnus. Whereas the aecidia on the Euphorbia 

 leaves discharged their spores to a height of 10-15 mm. and even 

 higher, the aecidia on the leaves of the Calystegia and the Rhamnus 

 discharged their spores to a height of only 4-6 mm. and, at most, 

 8 mm. It was also observed that the aecidia of Puccinia coronata 



