254 BIONOMICS 



having obtained a growth of soredia in about seven months; the latter, 

 starting with soredia, had a growth of well-formed squamules in nine months. 



It has been frequently observed that abundance of moisture facilitates 

 growth, and this is nowhere better exemplified than in crustaceous soil- 

 lichens. Meyer found that on lime-clay soil which had been thrown up from 

 a ditch in autumn, lichens such as Gyalecta geoica were fully developed the 

 following summer. He gives an account also of another soil species, Verru- 

 caria (Thrombium) epigaea, which attained maturity during the winter half 

 of the year. Stahl 1 tells us that Thelidium minutulum, a pyrenocarpous soil- 

 lichen, with a primitive and scanty thallus, was cultivated by him from spore 

 to spore in the space of three months. Such lichens retain more of the 

 characteristics of fungi than do those with a better developed thallus. Rapid 

 colonization by a soil-lichen was also observed in Epping Forest by Paulson 2 . 

 In autumn an extensive growth of Lecidea uliginosa covered as if with a dark 

 stain patches of soil that had been worn bare during the previous spring. 

 The lichen had reached full development and was well fruited. 



These facts are quite in harmony with other observations on growth 

 made on Epping Forest lichens. The writers 3 of the report record the finding 

 of " fruiting lichens overspreading decaying leaves which can scarcely have 

 lain on the ground more than two or three years; others growing on old 

 boots or on dung and fruiting freely ; others overspreading growing mosses." 

 They also cite a definite instance of a mass of concrete laid down in 1903 

 round a surface-water drain which in 1910 seven years later was covered 

 with Lecanora galactina in abundant fruit; and of another case of a Portland 

 stone garden-ornament, new in 1904, and, in 1910, covered with patches of 

 a fruiting Verrucaria (probably V. nigrescens). Both these species, they add, 

 have a scanty thallus and generally fruit very freely. 



A series of observations referring to growth and "ecesis" or the spreading 

 of lichens have been made by Bruce Fink 4 over a period of eight years. His 

 aim was mainly to determine the time required for a lichen to re-establish 

 itself on areas from which it had been previously removed. Thus a quadrat 

 of limestone was scraped bare of moss and of Leptogium lacerum, except 

 for bits of the moss and particles of the lichen which adhered to the 

 rock, especially in depressions of the surface. After four years, the moss 

 was colonizing many small areas on which grew patches of the lichen 2 to 

 10 mm. across. Very little change occurred during the next four years. 



Numerous results are also recorded as to the rate of growth, the average 

 being i cm. per year or somewhat under. The greatest rate seems to have 

 been recorded for a plant of Peltigera canina growing on " a mossy rock 

 along a brook in a low moist wood, well-shaded." A plant, measuring 10 

 by 14 cm., was deprived of several large apothecia. The lobes all pointed 

 1 Stahl 1877, p. 34. 2 Paulson 1918. a Paulson and Thompson 1913. 4 Fink 1917. 



