Emerson : Macrophoma and Diplodia ~>~)3 



similarity of their pycnidia. So it was with no little pleasure that 

 pycnidia were noticed on two seperate cultures, one pure Macro- 

 pJioma and the other pure Diplodia. Cultures on cocoanut pith 

 started January I ith showed on January 23d pycnidia with an 

 abundance of Macrophoma spores in each of the cultures, and on 

 February 12th there was obtained from the same pycnidium both 

 unicellular hyaline Macrophoma spores and bicellular brown 

 Diplodia spores. This is the average time that it takes a pure cul- 

 ture on the most favorable medium to develop, namely 10-12 days 

 for pycnidia with Macrophoma spores and 12-18 days more before 

 Diplodia spores are also abundant. There may be a slightly 

 earlier development of the two -celled spores in the pycnidia of 

 cultures from Diplodia spores than those from Macrophoma, but 

 in general there is no difference in appearance of mycelium, size, or 

 shape of spores or pycnidia. There certainly seems to be no 

 doubt that the unicellular white Macrophoma spores in the pycnidia 

 are simply the immature forerunners of the mature Diplodia spores. 

 In microtome sections of the leaf with the fungus growing on it 

 from a culture five weeks old, the cells near the pycnidium seem 

 much disorganized by the intercellular hyphal threads, being con- 

 tracted into irregular darkly-stained masses and the cell-walls 

 being difficult to trace. This affected area extends along the 

 lower part of the leaf to some distance on either side of the 

 pycnidium, but does not go through to the upper side. 



Material for microtome sections was put into weak Flemming's 

 solution to kill and fix. It was then washed in water, dehydrated, 

 and imbedded in paraffin. Some sections were mounted in 

 Canada balsam without any staining, but the Macrophoma spores 

 proved to be almost invisible and some of the Diplodia spores too 

 dark. As the pycnidia are very black an attempt was made to 

 decolorize the sections by putting them into hydrogen peroxide 

 and alcohol for about five hours. After washing they were stained 

 in saffranin, gentian violet and orange gentian and mounted in bal- 

 sam. This combination stains the Macrophoma spores orange 

 and the rest of the pycnidium brown, but care must be taken not 

 to overstain. The most satisfactory staining method was saffranin 

 ten minutes, Delafield's hematoxylin five minutes, washing out 

 excess of stain with acidified alcohol, and mounting in balsam. In 



