PDF - CES (IISc)

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MORPHOLOGY
podetial thallus was present, but Wainio 1 found in Cladonia sylvatica a
granular basal crust and, in Cladonia uncialts, minute round scales with crenate
margins measuring from -5 to I mm. in width. In some species (subgenus
Cladina) the primary thallus is quickly evanescent, in others it is granular
or squamulose and persistent. Where the basal thallus is so much reduced
as to be practically non-existent, apothecia are rarely developed and soredia
are absent Renewal of growth in these lichens is secured by the dispersal
of fragments of the podetial thallus; they are torn off and scattered by the
wind or by animals, and, if suitable conditions are met, a new plant arises.
Cladonia squamules vary in size from very small scales as in Cl. uncialis
to the fairly large foliose fronds of Cl.foliacea which extend to 5 cm. in length
and about i cm. or more in width. It is interesting to note that when the
primary thallus is well developed, the podetia are relatively unimportant
and frequently are not formed. As a rule the squamules are rounded or
somewhat elongate in form with entire or variously cut and crenate margins.
They may be very insignificant and sparsely scattered over the substratum,
or massed in crowded swards of leaflets which are frequently almost upright.
In colour they are bluish-grey, yellowish or brownish above, and white
beneath (red in Cl. miniata], frequently becoming very dark-coloured towards
the rooting base. These several characteristics are specific and are often of
considerable value in diagnosis. In certain conditions of shade or moisture,
squamules are formed on the podetium
basal squamules of the species.
; they repeat the characters of the
B. TISSUES OF THE PRIMARY. THALLUS
The stratose layers of tissue in the squamules of Cladonia are arranged
as in other horizontal thalli.
a. CORTICAL TISSUE. In nearly all these squamules the cortex is of
the "decomposed" type. In a few species there is a plectenchymatous
formation in Cl. nana, a Brazilian ground species, and in two New Zealand
species, CL enantia f. dilatata and Cl. Neo-Zelandica. The principal growing
area is situated all round the margins though generally there is more activity
at the apex. Frequently there is a gradual perishing of the squamule at the
base which counterbalances the forward increase.
The upper surface in some species is cracked into minute areolae; the
cracks, seen in section, penetrate almost to the base of the decomposed
gelatinous cortex. They are largely due to alternate swelling and contraction
of the gelatinous surface, or to extension caused, though rarely, by intercalary
growth from the hyphae below. The surface is subject to weathering and
peeling as in other lichens; but the loss is constantly repaired by the upward
growth of the meristematic hyphae from the gonidial zone ; they push up
1 Wainio 1880.