HYPOCREALES 



239 



contain sixteen spores. Their lowest representative connects directly to 

 the Melanospora-Nectria type. Thus in H. delicatula, the perithecia 

 stand comparatively irregularly on or in a slightly developed stroma 

 (Fig. 153). In other forms, the stromata have an even greater develop- 

 ment; thus, in the cosmopolitan H. citrina, they appear in the form of 

 irregularly formed, yellow or ochraceous, thin mats on earth, leaves or 

 tree trunks, often flat, up to one-half meter in cross-section. 



In the higher species, the stromata no longer form irregular crusts 

 growing indefinitely in all directions, but begin to be individualized: 

 they attain definite outlines and become fructifications. A first stage is 

 represented by H. rufa, whose stromata are still rather indefinitely 

 formed and spread over the substrate as flesh-colored, later red-brown, 



Fig. 154. — Hypocrea rufa. 1, 2. Sections through poorly and well-developed specimens. 



3. Habit. (Natural size; after Tulasne.) 



often confluent cushions (Fig. 154, 3). Under favorable conditions of 

 nourishment they are raised from the substrate by slight stipes and then 

 become differentiated into sterile portions directed toward the substrate, 

 and fertile portions directed away (Fig. 154, 2). The conidia of this 

 species cover the cultures with a greenish powder (Trichoderma viride). 

 They show a change in color similar to that of the conidia of numerous 

 other Hypocreales changing from greenish on acid to yellow on alkaline 

 media (Milburn, 1904). 



In a closely related segregate, Hypocreopsis lichenoides (Hypocrea par- 

 melioides, Hypocreopsis riccioidea) and H. Rhododendri, the stroma devel- 

 ops centrifugally into thick, subdichotomous lobes, resembling Parmelia 

 physodes. The perithecia are confined to the upper, outer surface and are 

 progressively developed as the lobes extend outward (Thaxter, 1922). 



