556 RESEARCHES ON FUNGI 



aecidia looked upwards. The material had been gathered for a day 

 or two before it came into my possession and had become somewhat 

 dry. The piece of leaf in the compressor cell, therefore, soon began 

 to absorb water through its edges. After about two hours from the 

 closing of the compressor cell, the aecidiospores began to be shot 

 out of their cups. I saw them strike and stick to the under surface 

 of the cover-glass, just as in Uromyces Poae, and many hundreds 

 of them were shot up to a height of 2-3 mm. 



Further observations were made with the help not only of a com- 

 pressor cell but also of a glass-ring cell which was 10 mm. high. 

 During the night, in one compressor cell a number of spores were 

 shot upwards to a height of 4 mm., while in the ring-cell a few 

 isolated spores were shot up 7-5 mm. My observations seem to 

 show that the maximum height of discharge for the individual 

 aecidiospores of Puccinia graminis is 7-8 mm. 



On focussing the top of the chains of aecidiospores in the cluster- 

 cups, I saw some of the spores discharged. At one moment a spore 

 could be seen at the end of its chain, at the next moment it suddenly 

 disappeared : its actual flight could not be observed. Sometimes 

 spores were shot away not individually but in groups of two, three, 

 or more. Several times the aecidia discharged what we may call 

 aecidiospore-bombs, i.e. clumps of spores some of which contained 

 60 to 150 individual spores. The sides of some aecidia seemed to 

 blow out like the side of a long-dormant volcanic peak which even- 

 tually suffers from a violent eruption, for along with an ejected 

 aecidiospore-bomb a larger or smaller fragment of the colourless 

 peridium was often carried. Some of the aecidiospore-bombs 

 landed on the under side of the cover-glass at a height of 7-8 mm. 

 above the aecidia, while others struck the side of a large ring-cell 

 at a distance of fully 1 cm. from the cup which had produced them, 

 thus affording evidence that they had been shot outwards with 

 considerable violence. In some of the ejected aecidiospore-bombs 

 more or less isolated chains of aecidiospores could be clearly seen, 

 from which fact we obtain some indication of the depth in the 

 aecidial crater at which the explosive force had come into existence. 

 When an aecidiospore-pustule was placed in a ring-cell so that the 

 tops of the aecidia were 7-8 mm. below the cover-glass, only a very 



