CARPOSPOREM. 



321 



fhallus 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 hyphae determine the 



ft 



Fig. 215.— Vertical section of the gelatinous thallus oi Leptogiiim scottnum (x 500); an epidermal layer clothes the 

 interior tissue, which consists mainly of amorphous and colourleis jelly in which lie the coiled chains of gonidia ; some of tlie 

 larger 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. ziT.—Usnea barbata. A longitudinal section of a slender 

 branch, soaked in potash solution ; B transverse section of an older 

 thallus-steni with the basal portion of an adventitious (or soredial) 

 branch sa (X 300) : s apex of the branch, r the cortex, x the axial 

 medullary bundle of hyphae, m the loose medullary tissue, s t'^e 

 gonidial layer. 



Fig. 216.— a branch of the thallus of 

 Ephebe pubescens (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 



