76 



THE GEOLOGICAL HISTORY OF PLANTS. 



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

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



Fig. Zb.—Megalopteris Dawsoni, Hartt (Erian, New Brunswick), a, Frag- 

 ment of pinna. 6, Point of pinnule, c, Venation, (The midrib is not 

 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 



