272 Count Gaston de Saporta on the Temperature 



§ 1. Examination of the Groups, Genera, and Forms with Tropi- 

 cal Affinities observed in the Ancient Floras. 



The vegetation of the Palseozoic strata does not with certainty- 

 include any of the existing genera. The attempts made in 

 Germany by some palaeontologists to assimilate to the living 

 ferns a portion of those of the Carboniferous formation seem to 

 be more specious than well founded*. They depend upon a 

 superficial affinity of form rather than upon identity of structure. 

 Moreover the positive analogies which this investigation has 

 sometimes brought out would tend rather to lead us to range 

 the ferns of this early age among the most exceptional tribes of 

 the existing order. It is thus, according to M. Brongniart f, 

 who is so cautious in his determinations, that the genus Scoleco- 

 pterisj Zenk., observed in the same state of chalcedonic petri- 

 faction as the species of Psaronius, and, like them, probably 

 contemporaneous with the coal-measures, resembles in the mode 

 of grouping of its capsules of fructification the genus Angiopteris 

 among the Marattiese, and that several species of Asterocarpus 

 resemble Kaulfussia, or only Gleichenia and Mertensia. Other 

 species of the same group seem to be allied to Matonia in the 

 tribe Cyathese. Lastly, the genus Senftenhergia, described by 

 Corda, appears to denote the existence of a Schizeacean. 



The much smaller proportion than was supposed of arbores- 

 cent species has weakened one of the arguments most frequently- 

 appealed to in favour of the supposed elevation of temperature 

 at this epoch. This applies also to the persuasion still enter- 

 tained by many geologists that a constant temperature of 25°- 

 30° C. (77°-86°F.) is necessary for the vegetation of tree ferns. 

 This cannot be supposed when we observe that under the tropics 

 it is principally in the hearts of mountain-forests and in the 

 bottom of elevated valleys that most of these plants grow ; their 

 region is situated between 400 and 600 metres, and extends 

 even to an elevation of 1000 metres. Moreover, according to 

 the testimony of Humboldt J, the arborescent ferns depart from 

 the equator towards the south as far as the forty-sixth and even 

 the fifty-third parallel ; they attain to an admirable development 

 in Van Diemen^s Land, at Hobart Town (lat. 42° 53'), with a 

 mean temperature of ll°-3 C. (= 54°'34 F.) — that is to say, 

 in an isothermic band of which the temperature is 2°*3 C. 

 ( = 4°-14F.) below that of Toulon. It is true, as is remarked 



* See especially * Die Farnkrauter der Jetztwelt zur Untersuchimg und 

 Bestimnmng der innern Formationen, &e.' von C. Hitter von Ettingshausen. 

 Vienna, 1865. 



t Tableau des Genres de Vegetaux fossiles, p. 27. 



X Tableau de la Nature, tome i. p. 166 (Galusky's translation: Paris, 

 1851). 



