MORPHOLOGY AND DESCRIPTION 23 



cells, the secondary sterigmata, forming a crown, or verticil, at the apex. 

 Each of the secondary sterigmata bears one chain of conidia. The mech- 

 anism shown in figure 3B would produce several times as many chains of 

 conidia as figure 3 A. Such a head as figure 3B would be compact, whereas 

 figure 3 A would represent a loose head. 



In figure 3A the cells in the single layer, each producing a chain of spores, 

 are in the strict sense the sterigmata. In figure 3B cells of the first layer, 

 or primary sterigmata, produce verticils of cells, the secondary sterigmata, 

 each of which is in the strict sense a sterigma. The cells are usually char- 

 acteristic in size and shape for series of closely related species. Where 

 there are both primary and secondary series, the primary sterigmata are 

 essentially supporting cells and vary much more in size and shape than do 

 the secondary sterigmata. For this reason they are more useful in species 

 diagnosis than the secondary series. 



Various usages are found in the literature. The primary sterigmata 

 are often called basidia. The secondary sterigmata are called phialids 

 because they have somewhat the shape of the pharmacists' phial (vial). 

 In translating descriptions into the Latin, Saccardo apparently followed 

 the describers verbatim, hence used no consistent terminology. We 

 find the primary sterigmata as sterigmata, basidia,. or pseudobasidia, and 

 the secondary series as sterigmata, pseudosterigmata, ramuli ("ramulis 

 sporiferis") or even rami (branches); all of these usages have been homo- 

 genized here into "primary and secondary sterigmata." 



Conidium Formation 



The actual spore-producing cell, or sterigma, is definitely specialized. 

 It ordinarily consists of an essentially cylindrical body, which, after 

 reaching a length more or less uniform for the species, narrows into a 

 spore-producing tube whose diameter is fairly uniform within the species. 

 Elongation is thenceforth confined to this spore-producing tube. The 

 nuclei in the sterigmata divide and one of each pair of daughter nuclei 

 passes into the tube; cell division follows. Parallel with the repeated 

 division of the sterigma nucleus, the tube continues to elongate rapidly, 

 successively cutting off new sections and pushing the older cells outward. 

 Each such chain of spores typically consists then of series of equal sections 

 cut from one tube or tip of a sterigma and each carries a daughter nucleus 

 derived directly from the active nucleus of the sterigmatic cell at the base 

 of the chain. No further divisions occur among the cells in the chains. 

 Such chains often contain several hundreds of spores, or conidia, each of 

 which is theoretically at least exactly like the rest, hence fully capable of 

 propagating the species (fig. 6). 



