125 



showed browning and incipient rot of the basal portion of the stem. Micro- 

 scopic examination and agar platings from these stems gave results identical 

 with those stated above. One plant that was so badly rotted in the pot 

 as to fall over was found bearing Helminthosporium conidia on its surface. 



Conidia produced in Moist-chamber Culture 



While stems with diseased lesions, either from the field or greenhouse, 

 when placed in an ordinary moist-chamber rarely gave Helminthosporium 

 conidia (or, if they did, only in small numbers), if the diseased stems were 

 placed on wet filter-paper in moist chamber and rather closely covered 

 with wet filter-paper Helminthosporium conidia invariably developed in 

 quantity on the lesions, the fungus eventually spreading throughout the 

 available wheat-tissue and producing conidia over the whole surface 

 (cf. with page 95). 



Evidence from Inoculation 



Severed, live wheat-shoots, grown under aseptic conditions, were placed 

 as under standard conditions (Appendix, page 180), except that the shoots 

 were not autoclaved but put, living, upon the inoculated agar. All such 

 shoots rotted rapidly and completely, the shoot being eventually covered 

 by Helminthosporium conidia. Since direct examination showed no 

 contamination, it is evident that H. No. 1 can cause rot of the wheat tissue. 



To determine the relative rotting power of this organism and other 

 Helminthosporiums under these conditions, fresh aseptic shoots of corn, 

 wheat, oats, barley, and rye were laid on washed agar with the growing 

 tip toward the circumference of the dish, and the cut end in contact with 

 the outer edge of the spreading mycelium of a colony about 5 cm. in diam- 

 eter. These were examined after 2 days and again after 5 days, and the 

 rate of browning was carefully calculated. In this way seventeen strains of 

 Helminthosporium were tested as to their ability to produce rot in live, 

 severed cereal-shoots. H. No. 1, the foot-rot organism, showed high 

 rotting ability, completely rotting a wheat shoot 11 mm. long in 5 days, 

 while H. No. 2 (H. ravenelii) produced no rot on any cereal. H. No. 1 

 rotted corn also, but much less rapidly than it did wheat, and its rate 

 on oats, barley, and rye was still less. Several other numbers showed 

 strong rotting power on wheat shoots, notably H. No. 10 (labeled H. 

 teres), isolated by Dr. Stakman from barley, H. No. 9 isolated by him 

 from wheat, and H. No. 13 (labeled H. sativum], isolated by Dr. Durrell 

 from barley. 



