AUSTRALIAN AND SOUTH SEA ISLAND STICTACE^. 261 



These peculiar gibbi or spots enable us to readily distinguish 

 the Stictaceae from any other folia ceous-Hchens and form the superfi- 

 cial characteristics of the family, and are easily seen with the 

 naked eye or by an ordinary pocket lens. 



These peculiar structural characters found on the under- 

 surface of the thallus are known as cyphellae, pseudo-cyphellae and 

 gibbi, according to their structure, and afford an excellent basis 

 for a natural system of classification of the numerous species of the 

 two genera, into groups or sub-groups, according to the form they 

 take. 



For example, if we examine those species with true Cyphellae, 

 it will be found that they are distinctly urceolate and appear to be 

 minute excavations in the substance of the thallus ; these are 

 usually quite free from soredia or powdery substance. 



The Pseudo-cypheilae, instead of being urceolate or hollow 

 excavations, are minute protrusions filled with minute whitish, 

 golden-yellow, or yellowish-gi'een soredia. 



In connection with these structures there seems to be a dif- 

 ference of opinion as to whether they are constant characters in any 

 given species, as will be observed by the following remarks by Dr. 

 Lauder Lindsay (33.420) : — " I am not satisfied that there is any 

 essential distinction (anatomical, morphological, or functional) 

 between Cyphellae and Pseudo-cyphellse. Though the former are 

 typically urceolate and smooth, they become pulverulent and 

 shallow; and pass thus, by imperceptible gradations, into the latter." 

 Having examined a very large series of specimens both in the 

 field under natural conditions in Australia, New Zealand, and 

 Tasmania, as well as numerous collections in herbaria, I have 

 experienced no difficulty in separating the species into their respec- 

 tive sections or groups by this character alone. 



Occasionally in very old specimens the soredia will be found 

 to have disappeared from a number of pseudo- cyphellae, but even 

 in these there is a distinct difference in the structures, and that 

 soredia will be found in the partially developed pseudo-cyphellae. 



In the pseudo-cyphellae group it will be found that in several 

 species the upper-surface of the thallus is also spotted with erumpent 

 soredia in a similar manner as the under-surface. This peculiar 

 chai'acteristic also affords a basis for a sub-group, which includes 

 5. argyracea and the alhed species. 



If we tear or cut across the thallus of one of these plants it will 

 be found that there is a difference in the colour of the tissues of the 

 thallus, as well as a decided difference in the structure. The upper 

 or cortical layer is composed of spherical or irregularly shaped cells, 

 then there is a bright green, bluish-green or yellowish-green layer 

 known as the gonidial-layer, and then a whitish or creamy-white 

 cottony layer, known as the medullary layer. 



The stratum of blue-green or bright chlorophyll-gi-een granules 

 are generally termed the gonidial-layer or algal-constituents of the 

 thallus, and are very similar in general out ine to several well-known 

 races of AIs^ce. 



