THALLOPHYTES 



79 



On the basis of habit, three types are recognized: (i) crustose lichens, with 



an undefined mycelium often penetrating the substratum; (2) foliose 



lichens, with a definite liverwort-like thallus, which has marginal 



growth and rhizoids (as 



Physcia, fig. 187, and 



Parmelia, fig. 188); and 



(3) fruticose lichens, 



which are erect and often 



branching (as Cladonia, 



the reindeer moss), or 



pendent and branching 



( Usnea'&g. 180). 



FIG. 188. Parmelia: an almost free foliose lichen 



Vegetative multiphca- on bark> showing cuplike apotnecia . 



tion is secured by soredia, 



which are scalelike or globular bodies, composed of a little tangle of 

 mycelium with some algal cells (figs. 1114-1116). The ascocarps are 

 very conspicuous structures, usually being apothecia (disklike forms), 



but some are perithecia. The hy- 

 menium is the usual mixture of asci 

 and paraph yses, and the ascus pro- 

 duces the usual eight ascospores. 



Sex organs. The sex organs of 

 the lichen fungus are evident in some 

 cases. The antheridia occur on 

 branching hyphae within a con- 

 ceptacle-like chamber called the 

 spermogonium. They are very small 

 cells that bud out and become ab- 

 stricted, suggesting conidia, as they 

 have often been considered. These 

 antheridia are cast off and function 

 directly as sperms, as is true of certain 

 of the red algae, and they are also 



FIG. i8g. Usnea: a pendent and called spermatia. 



branching fruticose lichen, bearing con- The female sex organ also suggests 



spicuously flaring apothecia. ,. , T . ,,. 



that of the red algae. It is a multi- 

 cellular filament spirally coiled and terminating in a filamentous ex- 

 tension to the surface of the thallus. The spirally coiled region has 

 been called the archicarp, and the filamentous extension to the surface 



