LICHEN ASCI AND SPORES 



187 



than in fungi; in many instances some or all of the spores in the ascus 

 are imperfectly formed, and the full complement is frequently lacking, 

 possibly owing to some occurrence of adverse conditions during the long 

 slow development of the apothecium. In the larger number of genera and 

 species the spores are small bodies, but in some, as for instance in the 

 Pertusariae and in some Pyrenocarpeae, they exceed in size all known fungus 

 spores. In Varicellaria microsticta, a rare crustaceous lichen of high moun- 

 tains, the solitary i -septate spore measures up to 3 50 /i in length and 1 1 S /i in 

 width. Most spores contain reserve material in the form of fat, etc., many are 

 dark-coloured; Zukal^ has suggested that the colour may be protective. 



Their ejection from the ascus at maturity is caused by the twofold 

 pressure of the paraphyses and the marginal hyphae on the addition of 

 moisture. The spores may be shot up at least i cm. from the disc'^ 



d. Spore Germination. Meyer" was the first who cultivated lichen 

 spores and the dendritic formation which he obtained by growing them on 

 a smooth surface was undoubtedly the prothallus (or hypothallus) of the 

 lichen. Actual germination was however not observed till Holle* in- 1846 

 watched and figured the process as it occurs in Physcia ciliaris. 



Spores divided by transverse septa into two or more cells, as well as 

 those that have become "muriform" by transverse and longitudinal septation, 

 may germinate from each cell. 



e. Multinucleate Spores. These spores, which are all very large, 

 occur in several genera or subgenera: in Lecidea subg. Mycoblastus (Fig. 105), 

 Lecanora subg. Ochrolechia and in Pertusariaceae. Tulasne* in his experi- 



Fig. 105. Multinucleate spore oi Lecidea 

 [Mycoblastus) sanguinaria Ach. x 540 

 (after Zopf). 



Fig. 106. Germination of multinucleate 

 spore of Ochrolechia pallescens Koerb. 

 X 390 (after de Bary). 



ments with germinating spores found that in Leca7iora parella (Ochrolechia 

 pallescens}) germinating tubes were produced all over the surface of the 

 spore (Fig. io6). De Bary" verified his observations in that and other species 

 and added considerable detail : about twenty-four hours after sowing spores 

 of Ochrolechia pallescens, numerous little warts arose on the surface of the 



iZukali895. = Fee 1824. 3 Meyer 1825. * Holla 1849. 



= Tulasne 1852. « De Bary 1866-1867. 



