CUCURBITARIA. 



207 



an acute beaked pore. Where the bark has been lost, a 

 good lens may distinguish the spherical or ovoid dark-coloured 

 perithecia. On the finer twigs the whole 

 bark is often perforated by numerous tiny 

 pycnidia, hardly distinguishable with the 

 naked eye. 



If these various forms of fructification be 

 submitted to microscopic examination, sections 

 through the yellow pustules will show them 

 to have that colour, because the transparent 

 periderm has become loosened from the rest 

 of the bark ; underneath the corky layers 

 will be found a red stroma of pseudo- 

 parenchymatous hyphal tissue. This stroma 

 by its growth causes a gradual rupture and 

 loosening of the corky and other layers of the 

 periderm ; wherever this takes place, conidio- 

 phores are developed, and give off numbers of 

 tiny, hyaline, ovoid or cylindrical conidia. 

 The stroma itself is somewhat spongy, and 

 encloses numerous cavities which also become 

 lined with conidiophores. At a later period 

 the tissue enclosing these cavities may become 

 dark coloured, so that structures similar to 

 pycnidia are formed. In such cavities the 

 red colour disappears, and the hyphae, coni- 

 diophores, and conidia appear transparent. 

 The real pycnidia appear later, and consist of 

 a peridium of coarse pseudoparenchyma con- 

 taining conidia similar to those just described 

 (Fig. 99, a). From the openings of these 

 pycnidia the conidia emerge as red tendrils, 

 rising as much as one centimetre above the 

 pore. Adjoining these forms of sporophore 

 just described will be found others : unde- 

 veloped perithecia with young asci ; dark- 

 brown pycnidia with brownish-grey, multi- 

 septate, compound conidia ; or similar pycnidia 

 with unicellular spherical, brownish-grey conidia. 



Where the disease has made further progress, the pustules 



Fig. i)S.—CafU)-lnUuia 

 laburni. Plant of La- 

 burnum (diagrammatic); 

 the branches 1, 2, 4 are 

 still living, and were in 

 full foliage during the 

 preceding suninier ; a, li, 

 c, d, e, places where the 

 rind is dead and the 

 cork-layer ruptured ; at 

 a and 'h the perithecia 

 are already developed, 

 and the mycelium has 

 extended into the wood. 

 (After V. Tubeuf.) 



