22 Robert S. Kikby 



cultures were made, in the comparative study of the fungus in pure cul- 

 ture from many sources. The growth of this fungus on various media 

 is in general of two types, examples of which are as follows: 



Type I: On 0.2-per-cent dextrose agar the growth (Plate III, A and 

 B) reaches 2.5 centimeters in diameter after seven days, and seldom 

 exceeds from 5 to 7 centimeters in thirty days or longer. The mycelium 

 after seven days of growth is submerged or wholly appressed. The colony 

 is translucent and is made up of feathery, rhizomorphic strands resembling 

 the feathery branchings of some mosses. After thirty days the appear- 

 ance of the colony is nearly the same as at the end of seven days, except 

 that it has become in color a deep neutral gray 8 and hyphal strands have 

 appeared near the center. The rhizomorphic strands are appressed to 

 the surface or submerged. Single hyphae radiate toward the edge of the 

 culture. The cells of the hyphae are from 16 to 45 /x long and from 4 to 

 5.5 /x in diameter, and contain from 10 to 25 guttulae. The cell walls 

 are hyaline. Branches arise near the tip of about every eighth to tenth 

 cell, or at a distance apart of about every 150 to 250 /jl. The cells of the 

 branches are much more variable in size and shape than those of the main 

 hypha, ranging from knob-like cells with a diameter of 5/i, such as occur 

 at the end of a few hyphae, to cylindrical cells resembling those of the 

 main hypha. 



Type II: On potato agar (5.4 pH) the growth (Plate III, E and C) 

 reaches 7 centimeters in diameter at the end of seven days, and covers 

 the plate (9 centimeters) in from eight to nine days. After seven days 

 of growth the mycelium is hyaline, and is submerged or wholly appressed. 

 The individual colony is abundantly and distinctly flexuous; its margin 

 is even but is not marked by a definite line, appearing finely frayed. At 

 thirty days the mycelium of the colony has assumed a more pronounced 

 aerial habit, rising to a height of 2 millimeters and growing on the sides 

 of the petri dish. The aerial growth causes the surface to appear as if 

 covered with a silvery bloom. The colony ranges in color from a neutral 

 gray to a deep neutral gray. The surface of the medium is thickly covered 

 with tortuous, mixed, ribbon-like, rhizomorphic bands of hyphae. These 

 bands are made up of from two to eight strands of parallel hyphae. 

 The cells of the individual strands are cylindric, and have thick, dark 

 neutral gray walls; they are 75 to 260 ju long and from 4 to 6.5 fi in 

 diameter (averaging 184 by 5 fj). The contents are hyaline and sparingly 

 guttulate. Nearly every cell in the strands sends forth a branch at its tip. 

 The cells of the hyphal strands closely resemble those of the plate mycelium 

 on the host (Plate III, C). The branches terminate in thin-walled hyaline 

 hyphae, the individual cells of which contain from 10 to 30 guttulae. The 

 cells are very variable in shape and size, ranging from 15 to 50 y. long and 

 from 2 to 6 m in diameter. Anastomosing is observed frequently. 



* Ridgway, Color standards and nomenclature- 



