PANUS STYPTICUS LUMINESCENS 413 



used so successfully in making the photograph of a fern leaf shown 

 in Fig. 171, p. 394. But the attempt was an entire failure ; for the 

 negative, when developed, after an exposure for 24 hours, was 

 uniformly white and showed no trace of a leaf whatsoever. 



As may be seen by comparing the photographs shown in 

 Fig. 170 (p. 391) and Fig. 175, the mycehum of North American 

 origin does not differ in external appearance from a mycelium of 

 English origin. Morphologically they are ahke, so that one cannot 

 tell them apart by their daylight appearance. Yet, physiologically, 

 they are so different that one glance at them in a dark room is 

 sufficient to enable one to determine their geographical origin. 



Hyphal Fusions between the Two Forms.— The myceha of 

 the two physiological forms of Panus styyticus in my cultures all 

 originated from many spores and resembled one another. Both of 

 them were found to consist of very slender hyphae bearing clamp- 

 connections at intervals, the presence of the clamp-connections 

 indicating that the mycelia were in the secondary or diploid phase 

 of their development. It seemed of interest to determine whether 

 or not the mycelia of the two forms would fuse with one another if 

 given the opportunity. Accordingly, two small pieces of mycelium, 

 one piece from P. stypt. luminescens and the other from P. stypt. 

 non-luminescens were placed near to one another in a hanging drop 

 of nutrient agar. Hyphae from each piece of mycelium grew 

 radially outwards through the culture medium, and soon luminous 

 and non-luminous hyphae began to cross one another (Fig. 176, A). 

 Thereafter, it was observed that hyphal fusions took place 

 between the hyphae of the two physiological forms ; and some of 

 these fusions are shown in Fig. 176, B, C, and D. In this figure, 

 purely for the sake of distinguishing the two forms from one another, 

 the hyphae of the non-luminous form Ijave been shaded, while those 

 of the luminous form have been left unshaded. In B and C, hyphal 

 fusions are shown at c, and in D at/, h, and m. The drawings were 

 made with the help of the camera lucida. 



The observations embodied in Fig. 176 show that the two 

 physiological forms of Pamts stypticus have mycelia which not only 

 resemble one another in microscopic appearance but which are able 

 to fuse with one another. This affords strong evidence that the 



