Phylum Inophyta [ 143 



Only the dikaryophase produces the specialized conidiophores called basidia, 

 which are regularly the seat of karyogamy and meiosis. There is a considerable 

 variety of types of basidia. Van Tieghem (1893) originated the terminology ap- 

 plicable to these; Martin (1938) has attempted to refine it, and Linder (1940) to 

 simplify it. 



Frequently, the seat of meiosis is a thick-walled resting spore or an otherwise 

 difTerentiated cell called a probasidium, upon which the proper basidium develops, 

 after meiosis, as an outgrowth. A basidium arising in this fashion is commonly 

 elongate and divided into four cells each of which produces a basidiospore. Such a 

 hypha-like basidium may be called a promycelium or a phragmobasidium; the latter 

 term is applicable also to an elongate four-celled basidium which does not arise 

 from a probasidium. In a few Basidiomycetes, the basidium is divided into four cells 

 by longitudinal walls; such basidia are called cruciate basidia. In the familiar 

 Basidiomycetes the basidium does not become divided by walls and is called a holo- 

 basidium or autobasidium. Gaumann ( 1926) distinguished two types of holobasidia: 

 the stichobasidium, in which the spindles of the dividing nuclei lie at various levels 

 and in various directions, and which frequently produces more than four nuclei; 

 and the chiastobasidium, in which the spindles lie transversely near the summit, 

 and which regularly produces just four nuclei. Dodge, translating Gaumann (1928), 

 denies much importance to this distinction. 



The meiotic divisions have repeatedly been studied. Apparent centrosomes have 

 been seen at the poles of the spindles (Lewis, 1906; Lander, 1933), but not by most 

 microtechnical methods (Savile, 1939; Ritchie, 1941). The chromosomes gather as 

 usual at the middle of the spindle and divide. The nuclear membrane becomes in- 

 distinct, but the nuclear sap remains distinct from the cytoplasm nearly until the 

 completion of division; it then disappears, leaving the groups of daughter chromo- 

 somes connected by a spindle of the appearance of a dark streak in the cytoplasm. 

 Ob:;erved haploid chromosome numbers include the following: 



Coleosporium, fideMoxczM (1914) 2 



Coleosporium Vernoniae, fide Olive (1949) 8 



Coj&rmuj, fide Yokes (1931) 4 



Eocronartium, fide Fitzpatrick (1918) 4 



&;frffa, fide Whelden (1935) 4 



Gymnosporangium, fide Stevens (1930) 2 



Melampsora, fide Savile (1939) 4 



Myxomycidium flavum, fide Martin (1938) 8 



Puccinia, fide Savile (1939) 4 



Transchelia, fide Savile (1939) 4 



Russula, fide Ritchie (1941) 4 



Scleroderma, fide Lander (1933) 2 



f/romycg'^, fide Savile (1939) 4 



Savile suggests that some at least of the reports of a chromosome number of 2 

 may have resulted from misinterpreted observations of one pair of choromosomes 

 behind another. 



Normally, only the two meiotic divisions, producing four nuclei, occur in the 

 basidium; exceptionally, there are further, mitotic, divisions, resulting in more than 

 four spores on the basidium. The basidiospores are usually borne on slender stalks 

 called sterigmata. Sterigmata and spores are formed by evagination of the wall of 

 the basidium; the nuclei migrate through the sterigmata into the spores. 



