CERATOSTOMATACEAE 205 



has continued to spread at an alarming rate and threatens to 

 ehminate the American elm. In 1932 Buisman (1932) found, bv 

 growing together on sterilized elm twigs certain stains isolated 

 from conidia, that perithecia characteristic of Ceratostomella are 

 produced. She also secured perithecia by inoculating elm 

 branches with paired strains; this evidence in its entirety is in- 

 terpreted to show that C. ztlmi is heterothallic. An account of 

 this disease and the developmental history of its causal fungus, 

 to which the student is referred, is available from the researches 

 of Clinton and McCormick (1936). Ahrens and his associates 

 (1935) have prepared a complete list of references to studies of 

 this disease, especially studies conducted in Europe. 



Ceratostomella fimbriata causes black rot of sweet potatoes. Its 

 "asci" are ephemeral; consequently the perithecial stage was long 

 regarded as the conidial fungus, Sphaeronenia fimbriata, as Elliott 

 (1925) has shown. The true conidial sta^e consists of endog-- 

 enously formed conidia that adhere in chains. An understand- 

 ing of the details attendant on perithecial formation has come 

 from studies by Elliott (1925) and Andrus and Harter (1933, 

 1937). Although a pair of closely associated organs is produced 

 to initiate the perithecia, it is not definitely determined that a 

 fusion of antheridium and ascoo^onium involving nuclear mio-ra- 

 ton occurs. Apparently by a crosier device a binucleate cell 

 arises from the subterminal cell of the ascogonium. As soon as 

 the hyphae have formed an envelope around the original asco- 

 gonium, its walls disintegrate, and the ascogonium appears as a 

 naked protoplast. The initial binucleate cell then proliferates, 

 and soon the interior of the perithecial cavity is filled wdth naked 

 cells or vesicles. Eventually paired nuclei in these unwalled cells 

 fuse to make the primary nucleus of the ascus. There then fol- 

 low three successive nuclear divisions. The immature spores are 

 delimited by a layer of cytoplasm, and all appear to have a com- 

 mon base of attachment. They are thus clustered; and, since 

 no well-defined ascus wall ever appears, there is none to be dis- 

 solved. The periphery of the ascus is merely a cytoplasmic 

 layer. 



Among the organisms responsible for blue stain of wood the 

 world over are several species of Ceratostomella, notably C. pil- 

 ifera, C. ips, C. phiriaimzdata, C. minor, C. pseiidotsiigae, and C. 

 piceaperda. They may penetrate sapwood by way of the rays; 



