SIGNIFICANCE OF CONJUGATE NUCLEI 



283 



the wall between an (A) and an (a) cell breaking down so that 

 the (A) and (a) cells combine to form a single cell. 



In support of Hypothesis No. 1, one may cite the illustrations 

 of two cells in a spore-bed uniting laterally to form a single binu- 

 cleate basal cell, as given among others by Christman ^ for Phag- 

 midium speciosum and Colley ^ for Cronartium ribicola. 



Hypothesis No. 2. The two haploid mycelia (A) and (a), on 



Fig. 149. — Hyphal fusions on the same mycelium in various 

 species of Uredineae. A, Puccinia on Carex hirta ; a 

 bridging hypha tmiting two hyphae in the aecidial 

 myceUum. B, Puccinia on Phragmites communis ; 

 C, Puccinia on Carex acuta ; and D, Melampsora on 

 Salix vim.inalis : meshes in the aecidial mycelium. 

 E, Puccinia graminis ; a mesh in the uredinial my- 

 celium. The drawings copied by the author from 

 W. Voss ("tjber Schnallen und Fusionen bei den Ure- 

 dineen," Ber. d. Deutsch. Bot. GeselL, Bd. XXI, 1903, 

 Taf. XIX, Figs. 1, 4, 5, 8, and 11) and rearranged ; 

 shading added to the walls of the epidermal cells 

 in A. Highly magnified. 



coming into contact, do not intermingle appreciably, but each 

 remains in the leaf-territory which it has grown through and more 

 or less exhausted. Hyphal fusions take place between the two 

 myceha (c/. Fig. 149), with the result that one or more (A) nuclei 

 move into the (a) mycelium and one or more (a) nuclei move into 

 the (A) mycehum. The (A) nuclei move along the hyphae of the 



1 A. H. Christman, " Sexual Reproduction in the Rusts," Botanical Gazette, 

 vol. xxxix, 1905, pp. 267-275. 



' R. H. Colley, "Parasitism, Morphology, and Cytology of Cronartium ribicola," 

 Journ. Agric. Research, vol. xv, 1918, pp. 619-660. 



