Lewis: Black Knot Disease of Dianthera 69 



concentric lines (Plate LIX, fig. 2). These lines serve to indi- 

 cate the number of crops of spores produced as they are formed 

 by the broken stubs or remnants of branches from which the 

 spores have fallen. Figure 2, Plate LIX, shows an area which 

 has borne six or seven crops of spores. This figure shows also 

 the shape and outline of the conidiophore layer. 



The conidiophores are somewhat branched, septate, packed 

 very closely together and bear spores at the tip and from very 

 short lateral outgrowths near the tip. They continue growth in 

 length by a lateral branch after the spores have fallen and the 

 broken stubs appear in cross section as distinct lines. The 

 conidiospores are unicellular, oval, hyaline and measure 10 to 15 

 by Sfji (Plate LXI, fig. 2). 



With, age this layer begins to slough away, giving the outer 

 surface a very rough ragged appearance. While the conidio- 

 phore layer is breaking down a differentiation takes place in the 

 deeper stromatic mass upon which it rests. In transverse sections 

 small cavities appear in the stroma. These are the beginnings of 

 the perithecia and by the time the outer layer of conidiophores 

 have disappeared they are almost fully developed. The peri- 

 thecia are numerous and closely packed together in the stroma. 

 They are somewhat elongated 475 to 550 by 300 to 350/x and pro- 

 duce rather long necks which open by a definite ostiole. The 

 broken remains of the conidiophore layer together with the necks 

 of the perithecia cause the ragged papillate character of the sur- 

 face as noted above. 



The asci are small, 50 to 65 by 10 to 15/x, thin-walled, and 

 spring from the bottom and sides of the perithecium. The spores 

 are eight in number, biseriate, unicellular, hyaline, allantoid, and 

 measure 6 to 9 by 2/a. There are no paraphyses (Plate LXI, 

 fig. 4). The perithecia do not develop definite walls but each 

 represents rather a loculus in the stroma (Plate LX, fig. 2). 



The cultural characters of the fungus are not at present known, 

 as all attempts to grow it in cultures have failed. Attempts were 

 made to isolate from both the conidiospores and the ascospores 

 as well as the tissue from the stroma but without success. 



