REPRODUCTIVE ORGANS 275 



B. Relation of Lichens to Fungi 



a. Pyrenocarpineae. In Phycolichens (containing blue-green gonidia) 

 and especially in the gelatinous forms, fructification is nearly always a more 

 or less open apothecium. The general absence of the perithecial type is 

 doubtless due to the gelatinous consistency of the vegetative structure ; it is 

 by the aid of moisture that the hymenial elements become turgid enough 

 to secure the ejection of the spores through the narrow ostiole of the peri- 

 thecium, and this process would be frustrated were the surrounding and 

 enveloping thallus also gelatinous. There is only one minutely foliose or 

 fruticose "gelatinous family, the Pyrenidiaceae, in which Pyrenomycetes are 

 established, and the gonidia, even though blue-green, have lost the gelatinous 

 sheath and do not swell up. 



In Archilichens (with bright-green gonidia), perithecial fruits occur 

 frequently; they are nearly always simple and solitary; in only a few families 

 with a few representatives, is there any approach to the stroma formation so 

 marked among fungi. The single perithecium is generally semi-immersed 

 in the thallus. It may be completely surrounded by a hyphal " entire '' wall, 

 either soft and waxy or dark coloured and somewhat carbonaceous. In 

 numerous species the outer protective wall covers only the upper portion 

 that projects beyond the thallus, and such a perithecium is described as 

 " dimidiate,'' a type of fruit occurring in several genera, though rare among 

 fungi. 



As to internal structure, there is a dissolution and disappearance of the 

 paraphyses in some genera, their protective function not being so necessary 

 in closed fruits, a character paralleled in fungi. There is a great variety of 

 spore changes, from being minute, simple and colourless, to varied septation, 

 general increase in size, and brown colouration. The different types may 

 be traced to fungal ancestors with somewhat similar spores, but more 

 generally they have developed within the lichen series. From the life of the 

 individual it is possible to follow the course of evolution, and the spores of 

 all species begin as simple, colourless bodies ; in some genera they remain 

 so, in others they undergo more or less change before reaching the final 

 stage of colour or septation that marks the mature condition. 



As regards direct fungal ancestors, the Pyrenocarpineae, with solitary 

 perithecia, are nearest in fruit structure to the Mycosphaerellaceae, in which 

 family are included several fungus genera that are parasitic on lichens such 

 as Ticothecium, Mullerella, etc. In that family occurs also the genus Stigmatea, 

 in which the perithecia in form and structure are very similar to dimidiate 

 Verrucariae. 



Zahlbruckner' has suggested as the starting point for the Verrucariaceae 



^ Zahlbruckner 1903. 



18—2 



