222 Transactions British Mycological Society. 



From these results it is evident that conidial stromata form 

 rapidly and mature quickly, the conidia being produced with 

 considerable speed. 



2. Pycnidial Stage. In autumn the fungus enters upon another 

 stage in its development. Amongst the conidial stromata other 

 stromata are to be seen, which are black and shiny, instead of 

 powdery, and lie mostly under the cuticle of the leaf. A low 

 magnification shows a number of papillae arising from the 

 stromata in a dark, rugose mass and marking the position of 

 developing pycnidia. At the apex of some papillae may be seen 

 a small orifice, through which pycnospores have been discharged. 

 The number of papillae arising from a stroma varies greatly 

 according to age. In the older and larger stromata as many as 

 thirty pycnidia are often present. The stromata may be as 

 large as 2 x i mm., but they vary in size considerably. 



Pycnospores are produced in great numbers from the interior 

 of the pycnidium, and when mature, are discharged in tendril- 

 like masses. The spores are oval and hyaline, and measure 

 5 X 1*5 /M. Pycnidial stromata are produced either by the 

 formation of a stroma at the end of a hyphal branch coming 

 from a conidial stroma or by the actual conversion of conidial 

 stromata into pycnidial stromata. In the first case the hyphae 

 extend horizontally a few cells from the parent stroma and 

 each sends out a mass of short, septate, hyphal branches, which 

 form a dense stroma having the usual pseudoparenchymatous 

 appearance. These pycnidial stromata extend more deeply into 

 the mesophyll of the leaf, sometimes even reaching the upper 

 epidermal surface. The lower epidermal and mesophyll cells 

 are destroyed by the fungus, the cuticle of the leaf alone covering 

 the stroma until maturity. In the second case the conidial 

 stroma extends further into the mesophyll, the hyphae become 

 more septate, and the whole stroma assumes a denser structure. 

 Most of the conidiophores break off at the level of the epidermis 

 of the clover leaf, and the stroma now presents the rugose, 

 papillate appearance already described; but usually there are 

 traces of the waved conidiophores characteristic of ordinary 

 conidial stromata. In one instance a pycnidial stroma was found 

 on the upper surface of the leaf, lying close to the midrib, and 

 connected by a thin weft of hyphae to a pycnidial stroma on 

 the lower surface. 



Pear-shaped pycnidial cavities are produced in the stromata 

 in great numbers, and are often only separated from one another 

 by a narrow wall of dark pseudoparenchymatous cells (fig. 5). 

 The first indication observed of a pycnidium is a colourless 

 pseudoparenchymatous mass of cells in amongst the darker 

 hyphae and below the surface. This mass of cells increases in 



