Of Cladonia Pyxidata

Bionomics.

The response of lichens to their environment is intimately associated with their physiological properties. Their scanty subsistence entails slow development though a few may he ranked as relatively quick growers—mostly soil lichens in touch with moisture. Such are Peltigera caning that spreads over damp lawns, etc., and crustaceous forms such as Baeomyces spp. Lecan ora tartarea, and Lecidea uliginosa; the latter has been known to spread over an area several feet in diameter in one season, and has been reported as a pioneer plant forming a dark film over sand dunes in Alberta. But in many lichens growth is often almost sta tionary : the large foliose Lobaria pulmonaria and the crustaceous Rhizocarpon geographicum have been observed to make practi cally no advance during a period up to 5o years. Accurate meas urements of more active Parmeliae, etc., have given a general increase of 1 cm. per annum; their fruiting bodies require in general four to eight years to develop.

Lichens do not grow on friable rocks or on peeling bark. They require, for the first stages at least, a substratum to which they can be firmly attached by filaments or by rhizinae. In fruticose branching and straggling forms compactness is often secured by haptera, which form a bridging connection between the fronds of the same lichen or to other vegetation, as for instance, Cladonia sylvatica, which becomes detached from the soil and adheres to the growing heather, thus securing not only attachment but light and air. Some few species become loose and continue growth while they drift about as erratic lichens. Several Parmeliae, Alectoriae, and Lecanora esculenta, etc., are erratic forms.

Phylogeny.

It would be interesting to know when the sym biotic plant originated and whether the first association of the fungus was with Myxophyceae or Chlorophyceae, but lichens, owing to the gelatinous nature of the thallus, become soft in water and there is little or no evidence in the rocks as to their antiquity: there is only a doubtful record of an Opegrapha in Mesozoic chalk. It is concluded from their elaborate morphology and physiology that they are very old plants, but the symbiotic organism—the lichen—is obviously of more recent descent than its component ancestors. Both symbionts are polyphyletic in origin : the algae

are blue-green or bright green ; the hyphae belong to various phyla of the fungi from which they are late derivatives. Basidiolichens are related to one fungus family, Telephoraceae; Ascolichens to Ascomycetes and to several distinct phyla within that class. There is no haphazard agglomeration of forms in the lichen group, but a closely related and easily recognized series of plant phyla. The ascophore, which marks the phylum, has undergone considerable alteration which is recognized in classification. Phylogenetic de velopment has, however, mainly taken place in the thallus which presumably began as a loose association of straggling hyphae with algal cells. It progressed to the definite crustaceous structure, and finally to the foliose and fruticose lichen. The greatest advance must have occurred when the thalline particle took an upward direction—a small outgrowth that was to develop into numerous forms.

The intimate relation between lichens and fungi is evident in the species that have remained on the border line. Some with scanty thallus appear to lose the algal symbiont as the ascophore matures, and the hyphae apparently revert to saprophytism as exemplified, for instance, in Calicium, a lichen genus, with Myco calicium, the fungal counterpart. Others classified now as lichens and now as fungi live on an alien lichen thallus though not always as simple parasites ; in a number of cases their hyphae penetrate the thallus and draw sustenance by symbiosis with the algal cells: these have been designated half-parasites. Lichen thalli are, however, a favourite host for many micro-fungi.

The main divisions of Ascolichens are traced to their fungal ancestors by the form of the ascophore : Pyrenocarpineae to Pyrenomycetes Coniocarpineae Graphidineae to Hysteriaceae Cyclocarpineae to Discomycetes Within these series is represented a number of phyla with an orderly progression of thalline structure. Both types of gonidia are sometimes represented in the same phylum and even in the same family e.g., Stictaceae.

The leading phyla of the different series are