SPHAERIALES 



289 



growth, while daylight or blue light are favorable to stromatal formation 

 (Freeman, 1910; Bronsart, 1919). 



The growing tip of the stromata remains white for a long time and is 

 covered with a strikingly regular hymenium of palisade-like conidiophores 

 which, if unicellular, cut off ovoid conidia; if they are multicellular, how- 

 ever, at any position they cut off fusiform conidia at their tips. In 

 cultures similar conidia are cut off directly on the mycelium. In two 

 American species, X. tentaculata and X. trachelina, the conidia do not 

 arise directly on the stroma itself but on special branches which grow like 

 coremia from the tips of the stromatal branches and fall off after shedding 

 their spores. 



Fig. 189. — Thamnomyces Chamissonis. (X %, after M oiler, 1901.) 



Long after the coremia have disappeared, as in the spring when X. 

 Hypoxylon (Fig. 188) has borne conidia in the previous fall, the stromatal 

 branches swell clavately in the upper part and proceed to form perithecia. 

 As far as is known, e.g., in X. tentaculata and X. trachelina (as in Hypo- 

 xylon coccineum; Lupo, 1922), this precedes the formation of an asco- 

 gonium without trichogyne, whose cells are first uni- or binucleate, later 

 multinucleate (Brown, 1913). 



Thamnomyces Chamissonis (Fig. 189), on hard, dry woods lying on 

 the forest floor, forms numerous caespitose, black, erect stipes of 1 to 2 

 mm. diameter which grow to 7 cm. without branching. Then they 

 branch five or six times dichotomously, the members becoming thinner 

 and shorter with every subsequent division. The level of each division 

 is nearly perpendicular to the previous; thus arise rigid trees up to 11 cm. 



