Thallophyta and Bryophyta 161 



Cercospora beticola is common on garden and sugar beets. Excise 

 the youngest lesions to obtain sections embracing healthy tissues as well 

 as diseased areas. If material must be killed in the field where an 

 aspirator is not available, use FAA, which gives adequate fixation. 

 Excellent preservation can be obtained with Craf III. Iron hema- 

 toxylin and safranin-fast green are the preferred stains. 



The wood- and bark-inhabiting pycnidia are handled like 

 perithecia of similar habitats. Such resistant subjects must be killed in 

 FAA, and butyl alcohol is the preferred dehydrant. 



LICHENS 



The lichens are found in a wide range of habitats, from the mist- 

 soaked rocks under a waterfall to the sun-baked face of a boulder. 

 Collections should include a portion of the substratum whenever 

 possible. Specimens usually are dried, and stored in containers that 

 prevent breaking of the fragile dry plant. If wet preservation is 

 preferred, use one of the fluids given in Chap. 10. Microtome sections 

 of the vegetative thallus have little justification. The association of 

 the green algal cells and the fungal mycelium is shown best by 

 dissections and freehand sections of fresh or preserved material. The 

 ascocarps should be preserved in fluid, examined with a hand lens for 

 general organization, and teased apart for examination of bits of the 

 hymenium under a microscope. 



Microtoming of the ascocarp is a vexing problem with most 

 species. The gelatin in the plant body becomes dry and brittle, and 

 the sections fail to ribbon and do not adhere well to the slide. Select 

 a species with a small, shallow cup-like apothecium. Kill in FAA and 

 dehydrate in butyl alcohol. Soak the embedded blocks in warm water 

 before sectioning. Staining presents no difficulties if selectivity for the 

 diverse components is not demanded. Safranin-fast green is probably 

 the best simple combination. 



Bryophyta 



The liverworts and mosses have such wide distribution and range 

 of habitat that some representative member of the group is usually 

 available for study. The most common liverworts are the aquatic 

 Riccia, the well-known Marchantia, and two rock-inhabiting species, 

 Conocephalum conicuni and RebonUa hemisphaerica. Anthoceros 

 seems to be less common, but it is easily overlooked if sporophytes are 

 not present. Large and conspicuous mosses are usually preferred, the 

 best-known ones are in the genera Polytrichiwi, Mnium, Catherinia, 

 Funaria, Rhodobrywn, and Sphagnum. Liverwort and moss species 



