76 THE GEOLOGICAL HISTORY OF PLAJJTS. 



various heights oa the stem, and which form a series of 

 stays like the cordage of a ship. This method of support 



Fig. 26.—Mipalopteris Dawsoni, Hartt (Erian, New Brunswick), a, Frag- 

 ment of pmna. i, Point of pinnule, c. Venation. (Tlie midrib is hot 

 accurately given in this figure.) 



still continues in the modern tree-ferns of the tropics 

 and the southern hemisphere. In one kind of tree-fern 



