Cryptogams or Flowerless Plants . 
H5 
Natural Order 
LICHENES. Tab. 107. 
D iagnosis.— Cellular persistent hygrometric plants dependent upon in¬ 
organic food, usually grey, yellow, or red, growing upon the ground, upon 
the bark and leaves of trees, or encrusting rocks or masonry. Fructification 
consisting of cells (asci) containing spores, collected in depressions or cavities 
of the thallus, which are probably rendered capable of germination (or 
perhaps of acquiring their full development) by the contact of microscopic 
corpuscles ( spermatid ) liberated by jointed filaments ( sterigmata ) contained 
in minute cavities or tubercles upon the same or upon a different thallus. 
Distribution. —A large group, represented in every quarter of the Globe, but by far most 
numerous in cool or Arctic climates, forming at extreme latitudes and elevations the very outposts of 
vegetation. Their growth is intermittent, depending upon sufficient humidity of the atmosphere; their 
friability in drought being a principal source of their destruction. 
VEGETATIVE Portion (thallus) either CRUSTACEOUS, spreading indefinitely from a centre, with lobed or wavy 
margin, and closely applied to the surface of stones, bark, &c., or FOLIACEOUS with free, ascending, irregularly-lobed 
segments, or FRUTICULOUS when ascending and irregularly branched so as to resemble a minute shrub. The thallus 
in the more typical Lichens, when examined in transverse section, exhibits 3 or 4 more or less distinct horizontal 
cellular strata, viz., 1st and uppermost, a cortical or epidermal coloured or colourless layer; 2nd, immediately under¬ 
neath a gonidial layer, containing minute green cells (gonidia) capable of reproducing the plant as buds ; 3rd, a 
medullary, entangled, filamentous layer ; and 4th, an under stratum from which the radicular fibres are developed. 
The thallus frequently contains crystals of oxalate of lime and also starch. 
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