VIOLENT DISCHARGE OF AECIDIOSPORES 557 



few individual spores and a few large bombs struck and adhered 

 to the under side of the cover-glass, while the majority of the spores, 

 after being shot up into the air at various angles, fell back again 

 either into the aecidial craters or on to the epidermis of the leaf 

 outside. Thus a distinct yellow halo of spores, 3-4 mm. wide, was 

 gradually formed around each aecidiospore-pustule. 



Upon a discharged aecidiospore, clinging to its outer wall, may 

 usually be seen one or more tiny colourless droplets. These do not 

 consist of water, for they do not rapidly evaporate, but their appear- 

 ance suggests mucilage. Up to the present I have not had an 

 opportunity to investigate them chemically, but I suspect that they 

 owe their origin to the intercalary cells in the aecidiospore-chains 

 and play a part in the phenomenon of discharge. 



(3) Puccinia pulverulenta. As before, small pieces of Willow- 

 herb leaf bearing aecidia were mounted on a tiny drop of water in 

 a compressor cell. Within five minutes of closing the cell aecidio- 

 spores were seen striking the cover-glass. Many spores were shot 

 upwards 2-3 mm., some 4 mm., but none 9 mm. A bomb of 

 about 50 spores was shot up 4-5 mm. Tiny colourless droplets 

 were seen clinging to the discharged spores, just as in Puccinia 

 graminis. 



(4) Puccinia Poarum (=- -P. epiphylla). A piece of a Coltsfoot 

 leaf containing an aecidium-pustule was mounted on a drop of water 

 in a ring-cell. Some of the aecidiospores were soon seen to strike 

 the under side of a cover-glass at a height of 7 mm. above the mouths 

 of the aecidia. Two ring-cells were placed one above the other and 

 a cover-glass on the top. After setting the piece of leaf at various 

 heights from the base of the compound cell, it was found that some 

 of the spores were discharged to a height of 1-1 cm. but none 

 to a height of l-S cm. When the outermost aecidiospores in an 

 aecidium were kept in focus, the discharge of individual spores was 

 observed. In its flight a spore often carried away one or more 

 loose spores which lay in its path. Little colourless droplets were 

 observed on all the discharged spores, as in Puccinia grajninis 

 and P. pulverulenta. 



In concluding this Section, a few general remarks may be added. 

 The curious structure of the aecidium with its peridium and its 



