Rate of Growth and Ecesis in Lichens 151 



partially shaded by shrubs on the east and by the rock face on the 

 west, the rock projecting over the area, which is seldom reached 

 by rain. Over a circular area of Lecanora fmstulosa 10 cm. across 

 and 1.8 m. from the ground, the apothecia and most of the epi- 

 lithic portion of the thallus were scraped from the rock, using the 

 hand lens to get minute apothecia and fragments of thallus. No 

 development was detected until 8 years had passed when several 

 small areas of thallus and a few apothecia 0.2 to 0.25 mm. across 

 were found. The hardness of the substratum and the lack of 

 moisture probably account for the unusually slow rate of de- 

 velopment. 



Primary Successions 



Ohio, area 15, a limestone 3.5 by 5.5 cm., largely imbedded in 

 the soil on a northward-sloping, mesophytic hillside, the rock sur- 

 face level with the soil to 2 cm. above, exposed to the sun. The 

 upper surface, covered mainly by Pannaria nigra and a moss, 

 was chipped on the side raised above the soil 1 to 2 cm. deep 

 over a quadrat 2 by 4 cm. After 2 years 4 minute areas of 

 Pannaria nigra were found within the quadrat, 2 of which bore 

 one minute apothecium each. After 5 years many more minute 

 lichen thalli were found in the quadrat, but they were too young 

 to be identified. After 7 years a half dozen areas of Pannaria 

 nigra were found. Apothecia were few in number. The largest 

 thallus was 1 cm. across and bore 6 well-developed apothecia. 

 The largest of these was 0.5 mm. in diameter. 



Kentucky, area 4, habitat like Kentucky, area 3. 9 In an area 

 of Biatorella simplex, a quadrat 10 cm. square was made by 

 chipping the rocks 2 to 10 mm. deep. After 4 years many minute 

 areas of thalli were found within the quadrat. After 8 years 

 many minute apothecia were observed under the hand lens. The 

 largest apothecia were 0.25 mm. across, while the largest in undis- 

 turbed areas surrounding the quadrat were 2 mm. across. 



Kentucky, area 2, on a limestone 8 by 11 cm., lying on dry soil 

 near the top of a steep, wooded hill about 200 m. high, the upper 

 surface of the limestone lying in a horizontal plane, with one of its 

 sides level with the soil while the opposite side was 9 cm. above 

 the soil. Verrucaria rupestris, Staurothele diffract ella, Pyre- 



9 See Kentucky, area 3, p. 142. 



