PDF - CES (IISc)

FAMILIES AND GENERA 311
b. Not gelatinous when moist.
^~\ XLl. PANNARIACEAE. Algal cells Nostoc, Scytonema or rarely bright-green,
'
Protococcaceae. Thallus crustaceous, squamulose or foliose.
XLll. STICTACEAE. Algal cells Nostoc or Protococcaceae. Thallus foliose,
XLIII.
and very highly developed, corticate on both surfaces.
PELTIGERACEAE. Algal cells Nostoc or Protococcaceae. Thallus
foliose, corticate above.
3. Lecanorine group (apothecia with a thalline margin).
The remaining families have all bright-green gonidia and nearly always apothecia
with a thalline margin. The group includes several distinct phyla :
XLIV. PERTUSARIACEAE. Thallus crustaceous. Apothecia, one or several
immersed in thalline tubercles ; spores mostly very large.
XLV. LECANORACEAE. Thallus crustaceous or squamulose. Apothecia mostly
superficial.
XLVI. PARMELIACEAE. Thallus foliose, rarely almost fruticose or filamentous.
Apothecia scattered over the surface or marginal, sessile.
XLVI I. USNEACEAE. Thallus fruticose or filamentous. Apothecia sessile or
shortly stalked.
N] XLVI 1 1. CALOPLACACEAE. Thallus crustaceous, squamulose or minutely fruti-
cose. Apothecia with polarilocular colourless spores.
XLIX. TELOSCHISTACEAE. Thallus foliose or fruticose. Apothecia with
polarilocular colourless spores.
L. BUELLIACEAE. Thallus crustaceous or squamulose. Apothecia (lecideine
or lecanorine) with two-celled, thick-walled brown spores (polarilocular in
part).
LI. PHYSCIACEAE. Thallus foliose, rarely partly fruticose. Apothecia with
two-celled thick-walled brown spores (polarilocular in part).
Subclass 2. Hymenolichens.
There are only three closely related genera of Hymenolichens, Cora,
Corella and
Dictyonema with Chroococcus or Scytonema algae.
There is reason to dissent from the arrangement in one or two instances which will
be pointed out in the following examination of families and genera.
B. FAMILIES AND GENERA OF ASCOLICHENS
The necessity for a well-reasoned and well-arranged system of classification
is self-evident: without a working knowledge of the plants that are
the subject of study no progress can be made. The recognition of plants
as isolated individuals is not sufficient, it must be possible to place them in
relation to others; hence the importance of a natural system. In identifying
species artificial aids, such as habitat and substratum, are also often of great
value, and a good working system should take account of all characteristics.
Lichen development is the result of two organisms mutually affecting
each other, but as the fungus provides the it is
reproductive system,
the
dominant partner : the main lines of classification are necessarily determined