THE THALLUS 289 



genus Pyrgillus has reached a somewhat similar stage of development, but 

 with a more coherent homogeneous thallus, while in Tylopkoron, also tropical 

 or subtropical, the fruit is raised above the crustaceous thallus but is thickl}' 

 surrounded by a thalline margin. The alga of that genus is Trentepohlia , 

 a rare constituent of Coniocarpineae. 



A much more advanced formation appears in the remaining family 

 Sphaerophoraceae. In Calycidium, a monotypic New Zealand genus, the 

 thallus consists of minute squamules, dorsiventral in structure but with a 

 tendency to vertical growth, the upper surface is corticate and the mazaedial 

 apothecia — always open — are situated on the margins. Tholurna dissimilis, 

 (Scandinavian) still more highly developed, has two kinds of rather small 

 fronds corticate on both surfaces, the one horizontal in growth, crenulate in 

 outline, and sterile, the other vertical, about 2 mm. in height, hollow and 

 terminating in a papilla in which is seated the apothecium. 



Two other monotypic subtropical genera form a connecting link with 

 the more highly evolved forms. In the first, Acroscyphus sphaerophoroides, 

 the fronds are somewhat similar to the fertile ones of Tholurna, but they 

 possess a solid central strand and the apical mazaedium is less enveloped by 

 the thallus. The other, Pleurocybe madagascarea, has narrow flattish branching 

 fronds about 3 cm. in height, hollow in the centre and corticate with marginal 

 or surface fruits. 



The third genus, Sphaeropkorus, is cosmopolitan ; three of the species are 

 British and are fairly common on moorlands, etc. They are fruticose in 

 habit, being composed of congregate upright branching stalks, either round 

 or slightly compressed and varjnng in height from about i to 8 cm. The 

 structure is radiate with a well-developed outer cortex, and a central strand 

 which gives strength to the somewhat slender stalks. The fruits are lodged 

 in the swollen tips and are at first enclosed; later, the covering thallus splits 

 irregularly and exposes the hymenium. 



Coniocarpineae comprise only a comparatively small number of genera 

 and species, but the series is of unusual interest as being extremely well 

 defined by the fruit-formation and as representing all the various stages of 

 thalline, development from the primitive crustaceous to the highly evolved 

 fruticose type. With the primitive thallus is associated a wholly fungal 

 fruit, both stalk and capitulum, which in the higher forms is surrounded and 

 protected by the thallus. Lichen-acids are freely produced even in crustaceous 

 forms, and they, along with the high stage of development reached, testify to 

 the great antiquity of the series. 



c. Thallus of Graphidineae. As formerly understood, this series 

 included only crustaceous forms with an extremely simple development of 

 thallus, fungi and algae — whether Palmellaceae, etc., or more frequently 

 Trentepohliaceae — growing side by side either superficially or embedded in 



s. L. 19 



