1919] STEVENS &- DALBEV—TREE FERN PARASITE 223 



fungus emerges and lays down a membrane one cell thick, of dark, 

 thick-walled, closely woven hyphae. Under this arise in a close 

 group numerous erect cells which in section appear like a palisade 

 formation (fig. 6). These cells elongate; the covering layer becomes 

 arched and eventually ruptures. The paUsade-like cells are really 

 conidiophores and bear the large, dark, i -celled spores (fig. 8). The 

 pycnidia are often sterile, the conidiophores then becoming greatly 

 overgrown and distorted. The conidia germinate upon the surface 

 of the leaf, producing at once an appressorium (fig. 9), which doubt- 

 less lends itself to the leaf invasion. This conidial structure is 

 clearly of the Leptostromataceae-Phaeosporae, but does not fit w^eli 

 any of the form genera there given. 



The infected spots give rise also to perithecia, although these 

 are much less abundant. The perithecia at maturity are high 

 and rounded (figs, iia, 11b, 14, 15). The perithecial wall is com- 

 posed of several layers of dark cells, compressed to a pseudo- 

 parenchyma (fig. 12). The perithecia are uniform in shape, with a 

 domed top; that they arise from the same mycelium which pro- 

 duces the pycnidia is clear (fig. 10) . The young perithecia are indis- 

 tinguishable from pycnidia, and indeed it appears that a pycnidium 

 which is not yet sporiferous can develop into a perithecium. The 

 first indication of differentiation is that in the perithecia a bed of 

 closely packed hyaline mycelium develops between the cuticle and 

 the covering. Soon the top begins to arch and to lay on internally 

 added layers in thickness. The pycnidium covering is only one cell 

 thick, the perithecium covering always several cells thick. At 

 maturity the perithecial wall is lined by a layer several strands 

 thick of felted hyaline mycehal threads. The asci, which are not 

 numerous, arise basally, various ages side by side, and interspersed 

 with numerous long mycehal threads (fig. 14) which may be re- 

 garded as paraphyses, although they are far from typical paraphyses 

 in appearance. The basal structure of both the pycnidia and the 

 perithecia consists of a dense mat of mycelium laid down in the 

 epidermal cells. This structure is difl&cult to represent because in 

 the growth process the epidermal cells are largely obliterated. The 

 facts, however, are hinted at in figs. 6, 12, and 15. It is this epi- 

 dermal subiculum which gives the radiating effect shown in fig. 18. 



