Jan. 14, 1918 Cultures of Wood-Rotting Fungi on Artificial Media 77 



more or less at right angles to the agar surface where the hymenium was 

 being developed. 



At first it was believed that the absence of pilei was probably due to 

 the fact that the tubes were left in a horizontal position and therefore 

 pilei had no chance to develop. The same results were obtained when 

 the tubes were placed vertically with the slant side facing the light as 

 when placed horizontally. Very recently, however, the writers have 

 devised a method by which small but otherwise typical pilei have been 

 grown on artificial media in the test tubes. The method was as follows : 

 In place of arranging the culture tubes so that the light fell directly on 

 the slanted surface the tubes were placed in one of two positions (i) 

 vertical in opaque boxes in such a manner that the rays of light would 

 fall on the tops of and parallel to the tubes and none on the sides or 

 bottom, and (2) nearly horizontal, with slanted surface of the agar 

 turned downward but ^^dth the light again falling only on the tops and 

 parallel with the tubes. Typical sporophores were produced by this 

 means for Polyporus dryophilus , P. hirsutus, and Fomes rimosus, the 

 only species tried so far. Whether this method will produce pilei with 

 all species is not known. There are objections to both methods where 

 one desires to obtain spores for plating in order to obtain individual spore 

 colonies — viz, when the culture tubes are kept vertically the discharged 

 spores fall on the agar rather than on the inner surface of the culture 

 tubes and when the culture tubes are kept nearly horizontal with the 

 slanted surface downward from the first the mycelium grows around the 

 edges of the agar onto the glass, thereby covering the surface of the tubes 

 where the spores will fall. There is also this further objection to both 

 methods — viz, that the agar in drying separates from the glass tubes in 

 a very irregular manner in place of from only the top surface as it does 

 when the tubes are kept horizontal with the slanted surface uppermost. 



INFLUENCE OF LIGHT ON THE FORMATION OF PILEI 



The pilei of the Polyporaceae always developed in such a manner that 

 their tops were directly toward the sunlight. Also the pilei of the 

 Agaricaceae when grown in cultures were strongly proheliotropic from 

 the very beginning of their formation. This positive heliotropism was 

 especially marked when the sporophores of Lentinus lepideus and Pleuro- 

 ius ostreatus were developing. The writers tried P. osireatus in three 

 different positions: (i) Culture tubes placed vertically but with the 

 lower part so shaded that the light entered at the top of the tube; (2) 

 tubes placed horizontally and covered with black paper so that the light 

 entered only at the top of the tube and this placed toward the light; 

 (3) the third experiment was made in a flask in which the medium was 

 slanted on the side of the flask. The flask was placed upright and the 

 development of the sporophores from this more or less slanting surface 

 was observed. In every instance from the earliest development of the 



