262 



MYCOLOGY 



spores in Phoma are colorless and unicellular. The pycnidia are 

 black with a terminal pore and depressed in the tissues of the host. 

 The genus is arbitrarily limited to those species in which the spores 

 are less than 15^, for the larger spored forms have been placed in the 

 genus Macrophoma. The most important species from the pathologic 

 viewpoint are out of the iioo species recognized the following: Phoma 

 betcB is the cause of the heart rot and blight of beets. Phoma batata 

 produces a dry rot of sweet potato; while Phoma solani behaves much 



nrn o 



Fig. 104. — Microscopic characters of apple blotch fungus {Phyllosticta solilaria). 

 I, vertical section of pycnidium showing pycnospores; 2, 3, 4, 5, mature pycnospores; 

 6, 7, 8, germinating spores; 9, mycelium. {After Scott, W M.. and Rorer, J. B., Bull. 

 144, U. S. Bureau of Plant Industry, pi. Hi, March 16, 1909.) 



like the damping-o£f fungus, attacking seedling egg plants near the sur- 

 face of the ground. The most destructive fungus of the genus Sphcerop- 

 sis is S. malorum which causes the decay of apples, quinces and pears 

 and attacks the stem of the apple tree producing characteristic cankers. 

 The genus includes about 180 species. The 150 species of the genus 

 C oniothyrium are widely spread geographically. The blight of rasp- 

 berry canes is due to Coniothyrium Fuckelii, which has only recently 

 come into prominence in the United States. The genus Septoria in- 



