134 TASM4VNIAIs[ LICHENS. 



2. The Examination of Lichens is a somewliat more 

 difficult matter. Althougli their anatomical parts are few, and 

 their various organs comparatively simple, these are often so 

 minute as to require the use of a microscope with a 

 good quarter-inch objective. The apotJiecium or fruit 

 is of various forms, but invariably contains thecce 

 or bags which hold the spores. The usual number 

 of spores in each theca is eight. When large they are 

 reduced even to one, and sometimes they are very minute 

 and numerous. The sjpermagones are small nuclei form 

 organs, containing and ejecting the sjpermatia, which are 

 very minute, and are supposed to fructify the apothecia. 

 The thallus, or vegetative part of the j^laut, is either crusta- 

 ceous or foliaceous. The latter is the tyjDical form, and is 

 generally composed of three strata — cortical, gonidial, and 

 medullary— of which the gonidial is specially characteristic. 



3. How TO Know a Lichen. — If it is desired to know 

 whether a plant is a lichen or not, cut off a minute portion of 

 the thallus and lay it on a glass slip. Moisten it with a drop 

 or two of water, and then bruise it down gently with a pen- 

 knife till it seems all melted down ; put on a small glass cover 

 and submit it to the microscope, as above. If it be a lichen, 

 there will be found small greenish or yellowish cells, with 

 transparent walls, called gonidia, or bluish cells without walls, 

 called gonimic granules. The latter are sometimes conglo- 

 merated in sacs of various sizes and shapes, or concatenated 

 like a necklace, or scattered more or less widely through the 

 substance of the plant. It -will be well to try several por- 

 tions in case the first examination shows none of these cells. 

 Some lichens, however, are nothing but apothecia, and grow 

 on the thallus of other lichens. The class to which these 

 apothecia belong is determined by their general likeness to the. 

 apothecia of other lichens. 



4. Classification. — This class of plants finds its place 

 between the algae and the fungi ; many obscure plants of the 

 lower forms being with difficulty distinguished from algae, 

 and many species having so strong an affinity to fungi that 

 it has often been a question whether they do not belong to 

 that class. 



^e family which bears the closest affinity to the algse is 

 that of the Collemacb^, so called from their gelatinous ap- 

 pearance (Ureek colle, glue) when moistened. Some of these, 

 indeed, which grow on maritime rocks and are washed daily 

 by the tide are very readily mistaken for algae. 



Closely connected with this family are the remarkable 

 Myeiangiace^ (Greek myrios, many, angion, vessel) of which 

 there are only two or three species known. 



