THE FUNGI WHICH CAUSE PLANT DISEASE 



591 



Ri geranii (West.) Fcl. on cultivated geraniums 



R. primulae Thiim. 



Spots rounded-angular, subochraceous, emarginate; conidio- 

 phores amphigenous, 50-60 x 5 jti, continuous, somewhat denticu- 

 late, rarely branched; conidia fusoid-cylindric, 20-30 x 3-6 n, con- 

 tinuous or 1-septate. On Primula.^* 



R. lactea (Desm.) Sacc. is on violets; 



R. heraclei (Oud.) Sacc. on cultivated Heracleums; 



R. onobrychidis P. & D. on leaves of sainfoin. 



R. cynarae Sacc. causes loss of artichokes in France and Africa. 



R. coleosporii Sacc. is on sweet potato in Porto Rico.^*' 



R. modesta Sacc. is recorded for the strawberry. 



R. narcissi Chit, and R. vallambrosse Br. & Cav. cause disease 

 of leaves and stalks of Narcissus.-™ 



R. goeldiana Sacc. kills twigs of coffee. 



Piricularia Sacc. (p. 589) 



Conidiophores simple, rarely branched, 

 conidia obclavate to pyrif orm, 2 to many- 

 septate, solitary acrogenous, hyaline. 



A small genus of parasites. 



P. grisea (Cke.) Sacc."^'"^ produces 

 pallid or water-soaked, spots on culms 

 and leaves, with age greyish; conidio- 

 phores in clusters of two or five from 

 the stomata, simple or rarely sparingly 

 branched, greyish, septate; conidia sin- 

 gle, terminal in scorpioid cymes, ovate, 

 2-septate, 24r-29 x 10-12 ft. 



It causes death of rice plant tissue and 

 the disease called "blast." If affected 

 leaves or stalks be placed in a damp at- 

 mosphere for about a day a delicate 



greyish fungus, the sporing mycelium appears. The fungus grows 

 well in culture and applied to the rice plants ^ves rise to the 

 typical disease spots. This species was originally described on 

 Digitaria sanguinalis and the form on rice has been called 



feS 



Fig. 396^ — Piricularia grisea. 

 a, conidiophores. b, ger- 

 minating spores. After 

 Fulton. 



