504 Scientific Proceedings, Royal Dublin Society. 



XL — Explanation of Plates. 



Plate XLV. 



Pig. 1 . A typically diseased Tomato plant at a comparatively late stage of attack. 

 The original roots are dead and decayed. A bunch of secondary 

 adventitious roots has been developed higher up, but these have also 

 become attacked by the fungus. The overground stem is shrivelled 

 up to and just beyond the point of insertion of the lowermost leaf, 

 which is dying. The leaflets of the leaf above this one are already 

 beginning to show the characteristic rolling upwards and inwards of 

 their margins. The remaining leaves are still normal. 



Pig. 2. An infection experiment. The central plant (control) was wounded 

 but not inoculated. It remained perfectly healthy. The two side 

 plants were wounded and inoculated with a pure culture of P. 

 cryptogm. Both became diseased. The one on the right has toppled 

 over, and the shrunken base of the stem is clearly visible. The one 

 on the left, although affected in a similar manner, was prevented 

 from falling by being supported . by a stake. The photograph was 

 taken four days after inoculation. 



Figs. 3-5. Photographs of the sexual organs of P. cryptogea developed in pure 

 culture on Quaker Oat-agar. A thick-walled oospore is present in 

 each case within the spherical portion of the oogonium, the funnel- 

 shaped base of which is still within the antheridium. The hyphae 

 bearing the oogonia and antheridia are not discernible. Pigs. 3 and 

 5. x 5-10. Fig. 4 is the same as fig. 5. x 850. 



Plate XLVI. 



Cross-inoculation experiments with P. cryptogea on Tomato (fig. 1), 

 Petunia (fig. 2), Aster (fig. 3), and Cheiranthus (fig. 4). In each 

 case the normal plant in the right-hand pot served as a control, 

 being wounded but not inoculated. The diseased plants in the 

 three pots on the left in each series were wounded and inoculated 

 in each case with pure cultures of the fungus isolated from Tomato, 

 Aster, and Petunia respectively, from left to right. 



