THE FLORA OF THE COAL FORMATION. 



401 



Fig. 174. — Trigonocarpum HooJceri, Dawson; from the Coal measures of Cape Breton. 



d 



A, Broken specimen magnified twice natural size. 



B, Section magnified: a, the testa; b, the tegmen; c, the nucleus; and d, the embryo. 



C, Portion of tlie surface of the inner coat more higlily magnified. 



Tissues of Plants preserved in the Coal. 



This subject has occupied much of my leisure time for some years, 

 and I have published the results of an extensive series of experiments 

 and observations on the Coals of Pictou and Sydney, in a paper on 

 the "Vegetable Structures in Coal," in the Journal of the Geological 

 Society of London, February 1860; and a still more extended series 

 on the numerous coals of the South Joggins, in my memoir on the 

 " Conditions of Deposition of Coal," December 18G5. I give here a 

 summary of results of these inquiries. 



The direct investigation of the tissues preserved in coal has been 

 pursued to some extent by Witham, llutton, Goeppcrt, Brongniart, 

 Bailey, Hooker, Quckett, Harkncss, and others. Two difficulties, 

 however, have impeded this investigation, and liavc in some degree 

 prevented the attainment of reliable results. One of these is the 

 intractable character of the material as a microscopic object ; the 



