The Rate of Growth and Ecesis in Lichens

Summary

One may speculate about possible or probable methods of migration to the denuded quadrats; but nothing is definitely known further than seeing parts of Cladonia thalli lying on some of the quadrats in early stages of ecesis. Other possible methods are through fragmentation, through soredia, and through spores. Some probable speculations regarding the means of ecesis might have been made for some of the studies, but this would have been scarcely worth while in the absence of definite data.

Many of the results recorded above cannot be summarized readily, and one must refer to the various studies for such data. Of data which are readily summarizable, the more important are given below.

Graphis scripta increased in diameter from 0.2 to 0.75 cm. in 1 year. Verrucaria muralis increased in diameter 0.6 cm. in 1 year. Physica pulverulenta increased in diameter for 7 years at the rate of 0.42 cm. per year. Parmelia borreri increased in diameter 1.3 cm. in 1 year. Parmelia caperdta increased in diameter from 0.625 to 1.3 cm. per year for 8 years. Parmelia conspersa increased in diameter for 7 years at the average rate of 1.16 cm. per year. Umbilicaria pustulata increased in diameter for 8 years at the average rate of 0.36 cm. per year. Peltigera canina grew 1.75 cm. in one direction in 1 year.

Biatorella simplex replaced apothecia removed from sandstone conglomerate in 4 years, and sterile Psora russellii growing on limestone produced apotheoia in the same time. An area of Peltigera canina deprived of its apothecia produced 12 young ones in 1 year. Smooth and sterile plants of Umbilicaria pustulata growing on high sandstone became strongly pustulate and produced apothecia in 7 years. Cladonia subsquamosa on sandstone conglomerate, when deprived of its podetia, regenerated them or produced others in 4 years. The same plant removed from the sandstone conglomerate, except minute fragments, produced squamules of normal size in 4 years and podetia of normal size in 8 years. Cladonia pityrea on rails, deprived of its podetia and squamules, except minute fragments, produced normal squamules in 1 year and numerous podetia in 3 years. Cladonia uncialis in a denuded quadrat on thin soil regenerated new plants of full size in 4 years, from fragments thrown over the quadrat.

Verrucaria nigrescens became established in a denuded limestone quadrat and produced apothecia in 6 years. Placodium aurellum became established on limestone and produced apothecia in 4 years. Placodium microphyllinum became established on a new plane-tree board in 2 years and produced apothecia in 6 years. Lecanora dispersa became established on limestone and produced apothecia in 6 years. Pyrenopsis schaereri and Collema pustulatum became established on denuded limestone in 8 years, and Placodium sideritis became established and produced apothecia in the same time. Pannaria nigra became established and produced apothecia on denuded limestone in 7 years. Endocarpon pusillum grew and became established and produced apothecia on limestone in 4 years. Amphiloma lanuginosum became established on denuded sandstone conglomerate and was plainly visible after 4 years. Cladonia pyxidata, C. fimbriata, and C. mitrula became established on soil in a denuded quadrat and reached normal size in 5 years. Cladonia pyxidata and C. cristatella became established on denuded rock and produced podetia and apothecia of normal size in 8 years. Cladonia subsquamosa became established on denuded sandstone conglomerate and produced podetia and apothecia of normal size in 8 years.

Certain crustose lichens become established and produce thalli and apothecia in denuded areas in 2 to 8 years. Foliose lichens increase in diameter from 0.3 to 3.5 cm. per year. Cladoniae regenerate squamules in one or two years and podetia in 3 or 4 years, and these plants become established by succession in 4 to 8 years.

So far as external appearance goes, lichens produce apothecia in their natural habitats in 1 to 8 years; but, except in instances of primary succession, it is not certain but that the primordia of apothecia were present within the thalli at the time that the various studies given herein were begun. From the studies of primary succession, it would seem that the full development of apothecia to the point when they assume their mature form requires from 4 to 8 years when the plants are growing in their natural habitats. However, much shorter times have been recorded for development in cultures.

Other similar data could be summarized. However, they would scarcely add to the conclusions regarding the rate of growth and ecesis in lichens, a subject about which so little has been known that one could scarcely form any opinion based on knowledge.