96 



DIFFICULTIES AND SOUECES OF ERROR. 



[CH. 



of microscopical sections or of the reproductive organs it would 

 be practically impossible to discriminate with any certainty 



Fig. 21. Polygonum Equisetifoi-me Sibth. and Sm. A. Showing habit of 

 plant. J nat. size. The two flowers towards the apex of one branch, drawn 

 to a larger scale in B. C. Node with small leaf and ochrea characteristic 

 of Polygonacete. From a plant in the Cambridge Botanic Garden. 



between fossil specimens of the plants shown in the drawings. 

 Examples such as these, and many others which might be cited, 



