149 



that no conidia indicating contamination were present, therefore, if the 

 colony were parasitized it must be either by a mycelium like that of 

 Helminthosporium and without conidia, or by some virus of un- 

 known character. To test this possibility well-established colonies of 

 H. No. 1 were inoculated with such striking saltants as M84. Transfers 

 of M84 were also made to points near the circumference of the H. No. 1 

 colony. If M84 bore a parasite of any kind this parasite might be ex- 

 pected to invade and overgrow the H. No. 1 colony. This it did not do, 

 but the two colonies halted a few millimeters apart in the manner char- 

 acteristic of two Helminthosporium colonies. It is quite clear that the 

 idea of colony parasitism is untenable in this connection. 



Position of inoculum. Since it was possible that the differing appear- 

 ances presented by the various sectors might be due to the position of the 

 mycelial strands in or on the agar, that is, on top of it, in it, or below it, 

 tests were made in three ways: 1, by placing conidia in an oese of w^ater on 

 the surface of poured agar; 2, by similarly placing conidia, without water, 

 in a shallow scratch made in the agar; 3, by so cutting the agar that a flap 

 about a square centimeter could be lifted and inoculated on the lower side, 

 that is, the side in contact with the glass, the flap being then put back in 

 place. These three modes of inoculation resulted in colonies of indistin- 

 guishable character. 



SALTATIONS FROM SINGLE CONIDIA 



Eight separate pure cultures were made from single conidia. The 

 eight colonies were under careful microscopic control from the time of 

 planting the conidia, through germination, and until the colony was well 

 developed, and it is certain that in each instance the colony was from a 

 single conidium. These pure strains, all alike in colony character, were 

 labeled Cl, C2, C3, etc. Well-marked saltants appeared in four of them 

 as follows: 



72 

 Cl 



110 



119 

 C2.. 120 



