112 MORPHOLOGY 



podetial thallus was present, but Wainio' found in Cladonia sylvatica a 

 granular basal crust and, in Cladonia undalis, minute round scales with crenate 

 margins measuring from '5 to i mm. in width. In some species (subgenus 

 Cladind) 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 CI. undalis 

 to the fairly large foliose fronds of CI. 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 CI. 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 ; they repeat the characters of the 

 basal squamules of the species. 



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 CI. nana, a Brazilian ground species, and in two New Zealand 

 species, CI. enantia f dilatata and CI. 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. 



