PANUS STYPTICUS LUMINESCENS 415 



two forms are very closely related to one another and indeed belong 

 to the same species. 



Since, from the recent observations of Mile Bensaude, Hans 

 Kniep, Miss Mounce, Vandendries, and others, it appears that 

 most Hymenomycetes are heterothallic, it is probable that Panus 

 stypticvs is also heterothallic. Assuming the truth of this sup- 

 position, it would be of considerable interest to obtain mycelia of 

 monosporous origin from P. stypt. luminesmns and from P. stypt. 

 non-luminescens, to cross them, and study their progeny. This would 

 enable one to determine whether or not luminosity and absence of 

 luminosity are a pair of unit characters which are inherited in a 

 Mendehan manner. It would also be of interest to find out which 

 of the two characters, if either, is dominant. It is possible that the 

 secondary (diploid) mycehum resulting from crossing two primary 

 (haploid) mycelia of opposite sex might be (1) always luminous, 

 (2) always non-luminous, or (3) sometimes luminous and sometimes 

 non-luminous. Unfortunately, up to the present, I have not had 

 sufficient leisure to attempt to solve these problems. 



Geographical Distribution of the Two Forms.— The geo- 

 graphical limits of the two physiological forms of Panus stypticus 



Fig. 17(5. — Panus stypticus. Hyphal fusions between luminous and non-luminous 

 forms. A, a lianging drop of nutrient agar, seen through the cover-glass of a 

 ring-cell, in which were planted side by side two mycelial masses, one derived 

 from a North American (Minnesotan) luminous form {P. stypt. luminescens), 

 and the other from an English non-luminous form {P. stypt. non-luminescens). 

 The illustration shows diagrammatically how the hypliae of the two forms grew 

 through the agar toward one another and crossed. B, C, and D, fusions between 

 a luminous and a non-luminous form as seen in a hanging drop of agar. Illus- 

 trations drawn with the camera lucida. To distinguisli the forms, the hyphae of 

 the non-luminous form have been shaded, while those of the luminous form 

 have been left unshaded. The breaks in the hyphae, at o o, indicate that, owmg 

 to lack of space, parts of the hyphae have been omitted in the drawing. The 

 arrows everywhere indicate directions of growth of the hyphae. B : a luminous 

 hypha, a, and a non-luminous one, b, growing in opposite directions, have united 

 by means of the bridging hypha c ; d, a clamp-connection ; e, an older clamp- 

 connection which has given rise to a lateral branch. C : the union of a luminous 

 hypha, a, with anon-luminous, b, by means of a bridging hypha, c, sent out from 

 a clamp-connection ; d, a clamp-connection which has just given rise to a lateral 

 branch. D : a luminous hypha a, from the clamp-connection b, sent out a 

 lateral branch c which, by means of a bridging hypha d, united with the non- 

 luminous hypha e at the point /. Continuing its course, the hypha c, in response 

 to a chemotropic stimulus, turnetl toward, and fused with, the luminous hypha 

 ff at the iioiiit h. The non-luminous liyiiha i, at the pointy', gave off a lateral 

 ijranch A-, wliich directed itself toward the luminous hypha I and fused with it 

 at the point 7n. Every hypha is now connected directly or indirectly with 

 every other hypha. n n are clamp -connections. The scale is 0-1 mm. long. 

 Magnification : A, a little less than 2 ; B, C, and D, 534. 



