THE AMERICAN 



MONTHLY 



MICROSCOPICAL JOURNAL 



YoL. IT. 



I^Ew York, ISTovembek, 1881. 



I^o. 11. 



An Introduction to the Study 

 of Lichens. 



BY REV. W. JOHNSON. 



{Concluded from page iSj.) 



Having, though but in a very lim- 

 ited way, touched upon the chief fea- 

 tures of the Lichen-thallus, we must 

 now endeavor to convey an idea of 

 its reproductive system. Lichens are 

 said to have many modes of repro- 

 duction. Korber enumerates six. Two 

 by spores and four by gonidia. But 

 without accepting that statement, the 



Fig. 46. 



Lichen undoubtedly has a secondary, 

 or indirect method, of reproducing 

 itself, by its green cells or gonidia. 

 Still, whether the gonidial cell alone 

 can produce a perfect plant, that is, 

 a plant which will bear fruit and 

 develop spores, we have not yet seen 

 authenticated. The proper and nor- 

 mal way of fructification in the Lichen, 

 is by sporidia. These are developed 

 in a special organ adapted for their 

 formation, protection, maturity and 



dispersion, when ripe. This organ is 

 denominated the apothecium. (Gr. 

 apo^Acke, a storehouse or repository.) 

 It is always found upon the surface, 

 or attached to the margin of the 

 thallus. It may be sessile — resting 

 upon the surface ; innate — sunk in 

 the thallus ; stipitate — on little 

 stalks, or surmounting the top of 

 podetia. These latter are cylindrical 

 and vertical prolongations of the 

 thallus, crowned with a cuplike cavity, 

 on the toothed margins of which grow 

 the apothecia, as in Cladonia. In 

 some cases the cup is substituted by 

 globose fruit, singly or conglomerate. 

 The apothecium assumes many diffe- 

 rent shapes on different plants. It is 

 typically round and flat, or slighly 

 concave — when it is termed scutel- 

 late. Sometimes it rises up from the 

 margin of the thallus like a target, as 

 in Peltigera j then it is peltate. At 

 other times, it is oblong and furrow- 

 ed ; when it is called lirellate. It 

 also appears like a little wart upon the 

 thallus, then it is verrucose. Besides 

 these, there are other forms. The 

 structure of the apothecium is the 

 most complex part of the plant ; and 

 it is beautiful in its arrangement, as 

 well as efficiently adapted for its pur- 

 pose of maturing and protecting the 

 spores. The apothecium consists of 

 two parts : an excipulum and a nu- 

 cleus, called the hymenium. The 

 excipulum is the outer covering, or 

 envelope of the apothecium. It is 

 seen encircling, or more or less enclos- 

 ing the fruit. When it is of the same 

 texture and color as the thallus it is 

 termed a thalline excipulum. But when 



