4160 - Witson: Nortu AMERICAN PERONOSPORALES 
yhich infests a tree, although a few species occur on shrubs. — = 
_ Perhaps this unusual habitat accounts for the rarity of the species 
in herbaria. 
On UtMacear : 
Celtis occidentalis District of Caliabia. * Waite 556,557. 
Type Locatity: Washington D. C., on Ce/tis occidentalis L. 
DistrisutTion: Maryland and District of Columbia. 
Icon: Jour. Myc. 7: pl. 77. f. 1-16. 
_ New YorK BOTANICAL GARDEN, 
