77 



III. THE DEVELOPMENT AND STRUCTURE OF THE SPORES. 



As far as has been observed, the spores of Ascolichenes are 

 formed in the same manner as the spores of the Ascomycetes. As 

 observed in Pertusaria communis the first stages of spore-formation 

 are identical with those in the fungus Peziza confine ns as recorded by 

 De Bary. The earliest beginnings of the spore-sac as seen in Per- 

 tusaria communis are distinguishable by the more granular and richer 

 plasmic contents of the sac as compared with those of the normal 

 hyphal cells ; as yet no nucleus is noticeable, but somewhat later 

 this organ appears as a spherical transparent highly refractive body. 

 With the growth of the spore-sac the plasmic contents advance more 

 and more toward the apex : the upper portion of the plasm contains 

 numerous small vacuoles ; the lower portion contains few or none 

 and is also less coarsely granular. The original nucleus now divides 

 into two, these into four and finally each one again into two, thus 

 making eight nuclei or spore mother-cells which in the majority of 

 lichens take a position in a vertical row, and each becomes enclosed 

 by plasm which is more translucent and granular than that of the 

 spore-sac. 



From this point developments differ materially, depending upon 

 whether the mature spore-sac will contain the normal number of 

 spores (eight) or fewer. In Pertusaria commttnis. the number of ma- 

 ture spores is one or two ; in this case it is found that only one or 

 two of the spore mother-cells or nuclei will continue to grow, the re- 

 maining six or seven not developing, and finally becoming partially 

 absorbed by the growing spore which in all cases is the one upper- 

 most. As the spore increases in size, it assumes more and more its 

 definite form ; the spore-wall also makes its appearance quite early 

 and increases in thickness and surface. As indicated above, the 

 eight nuclei develop into mature spores in the majority of lichens ; 

 those arriving at maturity take a definite position within the spore- 

 sac ; in the majority of cases being placed diagonally across the 

 sac parallel to each other. The elongated acicular and cvlindrical 

 spores usually extend longitudinally to the spore-sac and are often 

 attached to a dense gelatinous mass near the apex (Pe/tigera). 



Early in their development, all spores are simple and colorless 

 and their septation whether in one or two planes, begins very early. 

 This process requires further' study. The coloring substances of 

 spores may be deposited in the episporium (Caliciaceae) or uniformly 



