THE FORMATION OF HYPHAL FUSIONS 



9 



but that, when two mycelia of two different species are paired, they 

 interfere with each other's growth, grow toward, attack, and kill 

 individual interpenetrating hyphae, and never form hyphal fusions 

 with each other (Fig. 3). Reinhardt considered that all these signs 

 of antagonism support the view that Sclerotinia sclerotiorum, 

 8. trifoliorum, and S. tuberosa are three distinct species. 



In 1919, Laibach, 1 whilst studying the genus Septoria, isolated 



Fig. 3. — Struggle for existence between a mycelium of 

 Sclerotinia tuberosa (shaded) and a mycelium of Sclero- 

 tinia trifoliorum (unshaded) in an artificial culture 

 where the two mycelia were grown side by side. A 

 hypha of S. tuberosa, a, has grown into the mycelium 

 of S. trifoliorum, b, and is now being attacked by the 

 latter. The hypha b, stimulated morphogenically by 

 the hypha a, has sent out short branched branches 

 toward a, and these branches, stimulated tropically 

 by a, have grown toward a and are now applying their 

 ends to it and are beginning to envelop it. In the end 

 the S. trifoliorum hyphae will kill the S. tuberosa 

 hypha. The drawing copied by the author from 

 Reinhardt's Das Wachsthum der Pilzhyphen. 



two races (Stamme) of Septoria apii and observed that, whereas 

 the germ -tubes of conidia of one and the same race readily fuse 

 with one another, a germ-tube of one race and a germ-tube of the 

 other race, while exhibiting a tendency to fuse with each other, 

 never fuse in such a way as to leave no doubt that complete fusion 

 has taken place. A tendency to fuse, without fusion becoming 



1 F. Laibach, " Zur Kenntnis der Gattung Septoria," Ber. d. D. bot. Gesett., 

 Bd. XXXVII. 1919, pp. 2-47-248 ; also " Untersuchungen fiber einige Septoria- 

 Arten,' , Zeitschr.f. Pflanzenkr., Bd. XXXI, 1921, p. 189. In the latter communica- 

 tion lie mentions Septoria humuli and S. oenotherae as species which show no tendency 

 to fuse with one another ; and he also states that he thought of obtaining a chimaera 

 by isolating -fused hyphae of the two forms of Septoria apii, but did not succeed in 

 doing so. 



