LICHEN ASCI AND SPORES 



185 



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b. DEVELOPMENT OF THE ASCUS. The first attempt to trace the origin 

 and development of lichen asci and spores was made by Mohl 1 . He describes 

 the mother-cell (the ascus) as filled at first with a clouded granular sub- 

 stance changing later into a definite number usually eight of simple or sep- 

 tate spores. Dangeard 2 included the lichens Borrera (Physcia) ciliaris and 

 Endocarpon (Dermatocarpori) miniatum among the plants that he studied 

 for ascus and spore development. He found that in lichens, as in fungi, the 

 ascus arose usually from the penultimate cell of a crooked hypha (Fig. 104) 

 and that it contained at first two nuclei 

 derived from adjoining cells. These nuclei 

 are similar in size to those of the vegetative 

 hyphae, and in each there is a large nucleo- 

 lus with chromatin material massed on one 

 side. Fusion takes place, as in fungi, between 

 the two nuclei, and the secondary or defi- 

 nitive nucleus thus formed divides suc- 

 cessively to form the eight spore-nuclei. 

 Baur 3 and Nienburg 4 have confirmed Dan- 

 geard's results as regards lichens, and Rene" 

 Maire 6 has also contributed important cyto- 

 logical details on the development of the 

 spores. In Anaptychia {Physcia) ciliaris he 

 found that the fused nucleus became larger 

 and that a synapsis stage supervened during 

 which the long slender chromatin filaments 

 became paired, and at the same time shorter and thicker. The nuclear mem- 

 brane disappeared as the chromatin filaments were united in masses joined 

 together by linin threads which also disappeared later. At the most advanced 

 stage observed by Maire there was visible a nucleolus embedded in a con- 

 densed plasma and surrounded by eight medianly constricted filaments 

 destined to form the equatorial plate. A few isolated observations were also 

 made on the cytology of the ascus in Peltigera canina, in which lichen the 

 preceding ascogonial development is wholly vegetative. The secondary 

 nucleus was seen to contain a chromatin mass and a large nucleolus; in 

 addition two angular bodies of uncertain signification were associated with 

 the nucleolus, each with a central vacuole. The nucleolus disappeared in the 

 prophase of the first division and four double chromosomes were then plainly 

 visible. The succeeding phases of the first and the second nuclear division 

 were not seen, but in the prophase of the third it was possible to distinguish 

 four chromatin masses outside the nucleolus. The slow, growth of the lichen 

 plant renders continuous observation extremely difficult. 



1 Mohl 1833. 2 Dangeard 1894. 3 Baur 1904. 4 Nienburg 1908. B Maire 1905. 



Fig. 104. Developing asci of Physcia 

 ciliaris DC. x 800 (after Baur). 



