INTRODUCTION. XXXI 



preserved. The petrifactions associated are comparatively few in 

 number, and all are of the commoner type of petrified remains, 

 namely, woody stems, often of considerable size. Wood of the 

 Dadoxylon type, Psaronius brast'lienxis, and Lepidodend/ron Derby i 

 are practically the only petrifactions which have been recorded 

 from Gondwanaland, and consequently the anatomical structure of 

 most of the members of the Glossopteris flora is at present entirel)* 

 unknown. For this reason the botanical affinities of the flora are 

 less clear than in the case of the Northern Permo-Carboniferous 

 vegetation, where petrifactions of a special type, in which the 

 structure of more delicate organs such as small stems, leaves, cones, 

 seeds, etc., is preserved, are found on more than one horizon, and 

 have greatly added to our knowledge on this subject. 



"We may sum up broadly the results of our critical survey of the 

 botanical affinities of the Glossopteris flora, compared with that 

 of the Northern Hemisphere, as follows : — 



(1) The same great classes of plants are represented in each 

 flora, with the exceptions noted below. In describing the Glossop- 

 teris flora, we have no new types of vegetation to distinguish. 



(2) Of the six essentially Palaeozoic classes in the Northern 

 Hemisphere, two, the Lycopods and the Sphenophyllales, were 

 probably only represented in the Glossopteris flora by migrations 

 from the northern continent, and were not indigenous to 

 Gondwanaland. 



(3) One of the Palaeozoic classes, Cordaitales, and all the three 

 classes essentially of a Mesozoic facies, representing the incomings 

 of the types of vegetation developed in the Mesozoic rocks, viz., the 

 Cycadophyta, Ginkgoales, and Coniferales, may be regarded as 

 being represented by almost identical members in both floras. 



(4) The chief contrast between these two floras lies essentially 

 in the Fern-like plants, whether they be true Ferns or Cycadofilices, 

 and in the members of the class Equisetales, as well as in the 

 absence of indigenous representatives of certain groups. 



