CHAPTER V. 



REPRODUCTION AND PROPAGATION OF LICHENS. 



In the discussion of this subject only the established facts will 

 be considered. The hypothesis of the sexual origin of apothecia 

 and spores has already been briefly discussed, but it has been 

 sufficiently dwelt upon to enable the student to realize the con- 

 fusion that has been created in the systematic part of lichenology by 

 ascribing to the " male sexual organs " properties which they per- 

 haps do not possess, and of making them almost coequal with the 

 spores as a basis for classification. 



It is also well to anticipate a little by calling the student's attention 

 to the fact that structures of different groups of plants which are mor- 

 phologically similar may differ widely functionally. Such are the 

 spores of fungi and lichens. These great functional differences of 

 organs which are almost identical morphologically will be explained 

 in the discussion of lichen-spores, to enable the student to realize 

 why they are considered of such great importance in the system of 

 classification, while they are very unimportant physiologically. 



I. THE SPORES. 

 I. THE EJECTION AND DISTRIBUTION OF SPORES. 



There is little or no difference of opinion concerning the method 

 of the ejection and distribution of spores among lichens. Tulasne 

 has already recorded exact observations as to the manner in which 

 they are ejected and still more complete observations were made by 

 Ohlert. Both authors agree that the turgescent state of the hypo- 

 thecium and excipulum, aided no doubt by the paraphyses and the 

 gelatinous substance within the spore-sacs, produce the required 

 mechanical action to force the spores out of these organs. The 

 spores escape from the apex of the spore-sac by the rupturing of the 

 apical wall ; sometimes a cap-like segment is torn across, as in 

 Pertusaria and other genera. The method of opening or rupturing 

 is by no means constant in a given group or even in a given plant or 

 apothecium. As already stated, in the Caliciaceae the upper portion 

 of the spore-sac is entirely dissolved even before the spores are 

 3 87 



