CARPOSPORE/E. 
321 
thallus may either be determined by the gonidia, the hyphae being concerned only in a 
secondary degree in its construction, or it may happen that the hyphse determine the 
Fig. 215.— Vertical section of the gelatinous thalius oi LeptOi^iwn scotüiinn (X 500); an epidermal layer clothes the 
interior tissue, which consists mainly of amorphous and colourless jelly in which lie the coiled chains of gonidia ; some of tlie 
larg-er cells of the chains are colourless ; between them run the fine hyphae. 
form and mode of growth, while the gonidia have only a secondary share in the forma- 
tion of tissue. The former is the case in only a few Lichens; the latter is much 
Fig. 217. — Usnea barhata. A longitudinal section of a slender 
branch, soaked in potash sokttion ; B transverse section of an older 
thallus-stem with the basal portion of an adventitious (or soredial) 
branch sa (X 300) : j apex of the branch, r the cortex, x the axial 
medullary bundle of hyph», the loose medullary tissue, g the 
gonidial layer. 
Fig. 216.— a branch of the thallus of 
Ephebe piibcscciis (X 550). 
the more common, and is that of the typical Lichens, especially of those that are 
heteromerous. In some homoiomerous gelatinous Lichens (as Fig. 215) it appears 
Y 
