MORPHOLOGY AND PHYSIOLOGY. 47 



former case, the following structures are discernible in 

 a vertical section. The uppermost layer forming the 

 disk, consists of the spore-sacs and paraphyses. The 

 former are specialized hyphae which contain the spores ; 

 the latter are also specialized hyphae, placed vertically, 

 like the spore-sacs, but are much more slender and do 

 not contain spores. This layer is known as the thecium ; 

 the spore-sacs are also known as thecce or thekes. The 

 term spore-sacs is, however, preferable, as it expresses 

 more clearly what they are. The upper ends of the 

 paraphyses are frequently colored, as brown, black, 

 scarlet, yellow, etc., giving the disk its characteristic 

 color, as discerned by the naked eye. Below the the- 

 cium occurs the hypothecium, which consists usually, 

 of closely united hyphae, generally extending at right 

 angles to the spore-sacs and paraphyses. This tissue 

 is more or less cup-shaped ; in the Pyrenomycetous 

 type, it formes a sphere, enclosing the thecium. In 

 some cases it is convex, rather than concave or cup- 

 shaped, as in Cladonia and Bceomyces. 



If we have made our section from near the margin 

 of the cup, we will find the following additional tis- 

 sues. 1. Medullary tissue similar to, and continuous 

 with the medullary tissue of the thallus. 2. Cortical 

 tissue similar to and continuous with the upper corti- 

 cal layer of the thallus. Sometimes this layer is not 

 cortical. (Plate IV.) 



2. The Thalline Type. 



This differs from the foregoing in that the algal 

 layer of the thallus extends into the apothecium, 



