8 PALiEONTOLOGICAL BOTANY. 



for instance, the presence of scalariform tissue, or of 

 punctated woody tissue, lias been satisfactorily shown under 

 the microscope, we are entitled to hazard an opinion as 

 to the affinities of the fossils. In many instances, how- 

 ever, external appearances are the only data on which to 

 rely for the determination of fossil genera and species ; and 

 rash conclusions have often been drawn by geologists who 

 have not been conversant with the structure of plants. The 

 Araucaria markings point out the need of care in drawing 

 conclusions, and their variations at different parts of the bark 

 indicate the danger of a rash decision as to species. There 

 can be no doubt that in vegetable Pala3ontology the number 

 of species has been needlessly multiplied — any slight variation 

 in form having been reckoned sufficient for specific distinction. 

 We can conceive that the Araucaria bark markings in a fossil 

 state might easily supply several species of Lepidodendron. 

 A naturalist, with little knowledge of the present flora of the 

 globe, ventures sometimes to decide on an isolated fragment. 

 Hence the crude descriptions of fossil vegetable forms, and the 

 confusion in which Pala3ophytology is involved. Every geo- 

 logist who examines fossil plants ought to be well acquainted 

 with the minute structure of living plants, the forms of their 

 roots, stems, leaves, fronds, and fructification ; the markings 

 on the outer and inner surfaces of their barks, on their stems, 

 and on their rhizomes ; the localities in which they grow, and 

 the climates which genera and species affect in various parts 

 of the world. (Professor Balfour in the Proceedings of the 

 Royal Society of Edinburgh, April 1862, vol. iv. p. ^77*) 



Mode of Preservation of Fossil Plants. 



The mode in which plants are preserved in a fossil state may 

 be referred to four principal classes : — 1. Casts of the plants ; 

 from which all the original substance and structure have been 

 removed subsequently to the burial of the plants, and to the 



