Vol.. 1] Reed. — Two New Ascomycetous Fungi. 153 



The penetration of the fungus mycelium into the frond and 

 its contact with the algal cells, seem to act as an irritant or 

 stimulant upon the cells, and cause them to divide in a plane at 

 right angles to the usual division. In this way the frond becomes 

 distromatic or polystromatie. As the mycelial threads increase 

 in number, and the cells are more fully invested and isolated 

 from each other, this division continues until each half has 

 divided two or three times and "tetrads" are finally formed. 

 After the final division the "tetrads" are completely inclosed in 

 their capsules of interlaced mycelial threads. 



The perithecia are scattered irregularly over the surface of the 

 frond from the base to the apex and vary both in size and shape. 

 They are usually hemispherical or sometimes slightly mammillate 

 and brown to black when mature. The external diameter of the 

 perithecia varies from 273-450 /*, and the internal diameter 

 from 110-216 h-. In the cross section (cf. Fig. 14, PL 16) 

 the perithecium lies in the center half-way between the upper and 

 lower surfaces of the frond where there are but few scattered 

 algal cells. At the sides of the perithecium the tetrads have 

 been pressed together and In-oken up by the growth and expan- 

 sion of the central nucleus, and the final development of the 

 perithecial wall. The scattered cells on the upper and lower 

 surfaces of the perithecium are flattened slightly and their tetrad 

 arrangement completely destroyed by the expansion of the peri- 

 thecium . The perithecial walls are of medium thickness and are 

 pigmented on the upper part about the ostiole and also at the 

 base opposite. The inner, subhymenial layer is full of proto- 

 plasm and thin walled and is pseudoparenchyma, not well defined. 

 This gradually changes to well defined thick- walled pseudoparen- 

 chyma as it passes outward toward the exterior, the thickest walls 

 and deepest pigmentation being toward the outer surfaces, there 

 being little or no pigmentation at the sides of the perithecium. 

 The thick- walled pseudoparenchyma gradually shades into the 

 interwoven mycelia about the outer perithecial wall, and the 

 mj-celial branches project outward from its surface into the 

 cortex or joins with the medullary threads at the sides continuing 

 the center of the frond until interrupted by another perithecium. 



The perithecium first arises from a mass of hyph£e rich in 



