INTRODUCTION. 1 1 



sodium carbonate was not without success ; but F. Schulze J obtained much 

 more important results by maceration with the fluid which is named after 

 him, and by subsequent treatment with ammonia. In this way, especially 

 if the treatment is continued for a long time and the temperature is not 

 raised, it is in fact possible to isolate fragments of tissue in large quantities 

 from most kinds of coal. I have seen single scalariform tracheides and 

 groups of the same, and spores of every kind in excellent preservation in 

 original preparations by Schulze, and have convinced myself by repeated 

 trials of the suitableness of this mode of proceeding. The method has been 

 quite recently improved by Giimbel 2 , who has substituted absolute alcohol 

 for ammonia in washing the specimens, since it was found that parts still pre- 

 served and showing the form of the remains were dissolved by the ammonia. 



The tissue-remains which can be thus isolated in the coal are in the 

 great majority of cases such parts of the plant as have their membranes 

 strongly cuticularised, spores for example, and bits of cuticle which show 

 the gaps for the stomata. These objects are in general well preserved, 

 though great caution must be observed in judging of the details of their 

 form, because cuticularised membranes from a certain plasticity which they 

 possess are apt to suffer changes of form, which long experience alone can 

 enable the observer to recognise as artificial with any degree of certainty. 

 It will be an important work to examine the epidermal structure of the rind 

 of coal in known fossils on a more extended scale with the aid of the 

 methods here described, since comparatively little can be learnt- on this point 

 from thin slices. We owe much the largest part of what has been done in 

 the way of this examination of the epidermis to the labours of Schenk, 

 who has been careful in all cases to examine the carbonised coating of the 

 impressions, and has generally obtained connected shreds of cuticle, even 

 where the component parts of the rest of the tissue could no longer be 

 distinguished. Fragments of the membrane of highly lignified elements, 

 scalariform tracheides for example, are much less frequently obtained ; at 

 the same time they are always almost entirely unchanged, showing pits 

 and bordered pits sharply defined. Their fragile nature, for they split up 

 into diminutive angular pieces, explains perhaps the rarity of their occur- 

 rence. Spiral tracheides and sclerenchyma-cells out of shape are observed 

 here and there, while ordinary parenchyma is scarcely ever seen. Much 

 useful information on these points is to be found in Reinsch's 3 work, only 

 we must disregard his interpretations. 



We may now proceed to consider how far the results obtained by 

 many observers from the examination of the coal-seams themselves go 

 to prove that compact coal is composed of the fragments of plants. These 

 results are to be seen collected together in Goppert's 4 larger treatise, where 



1 F. Schulze (1). 2 Giimbel (2). 3 Reinsch (1). 4 Goppert (14). 



