VIOLENT DISCHARGE OF AECIDIOSPORES 555 



(1) Uromyces Poae. The first experiment was made by Mr. 

 W. B. Grove and the author working in conjunction. The leaves 

 of the Buttercup were laid out in a dish so that the aecidia looked 

 upwards, and slides smeared with glycerine were set above them. 

 The spores were shot upwards : for, a day or two after the beginning 

 of the experiment, many of them were found stuck to the under 

 side of the slides at a height of 2-3 mm. above the cluster-cups, 

 while others were seen to have collected on the leaves in a zone around 

 the cluster-cups. The maximum vertical distance of discharge 

 observed was 9 mm. At the end of 3-4 days, the cups were empty 

 almost to their base. 



On June 7, I collected some Buttercup leaves bearing Uromijces 

 Poae and, the next morning, placed a portion of a leaf flat in a 

 compressor cell {cf. Fig. 103, p. 240), so that the aecidia looked 

 upwards. A small drop of water was then added to the preparation 

 in such a way that it did not touch the aecidia. After closing the 

 cell and pressing the lid down to within about 1 mm. of the upper 

 surface of the leaf, I perceived with the low power of the microscope 

 that the cups were almost empty, most of the aecidiospores having 

 been discharged. Nevertheless, spore-discharge was still in progress ; 

 for, on focussing the cover-glass, I saw some of the remaining spores 

 strike and stick to its under surface. In the course of 24 hours 

 several hundred spores collected in this way, thus forming an orange 

 spore-deposit. It became evident that the aecidiospores were 

 being discharged one by one in succession, and not as clouds com- 

 I)arable with those produced during the puffing of Pezizae, and that 

 the discharged spores were turgid. 



(2) Puccinia graminis. Notwithstanding the large amount of 

 attention which has been paid to Puccinia graminis as the cause of 

 Black iStem Rust Disease of wheat and other cereals, hitherto, so 

 far as I know, no one has ever observed tlie violent discharge of the 

 aecidiospores. 



On June 19^, with the help of a jiair of scissors, I cut out from 

 a Common Barberry leaf a small piece of lamina upon which were 

 a iunnl)or of aecidia (r/. Figs. 22") and 22(5, pp. 5.^)1 and 5.12). and 

 mounted tiie piece of leaf on a small drop of water in a compressor 

 cell, so that the cut edges of the piece of leaf were wetted and the 



