208 



HEREDITY AND EVOLUTION IN PLANTS 



vi-rnaiion. have a pinnately compound blade, and leaflets 

 with pinnate dichotomous venation. Two or three years 

 later another botanist, examining it more closely, pro- 

 nounced it a "fern-like Zamia or a Zamia-like fern." 

 These facts show how puzzling the specimen was, and how 



(S no ) 



S36fl. 



FIG. 92. To the left, Cacadeoidea dacotensis Macbride. Longitudinal 

 section of a silicified specimen of a bisporangiate cone (unexpanded flower), 

 so taken that the pinnules of the microsporophylls on both sides of the 

 central axis, or receptacle, are successively cut throughout their entire 

 length. The lines indicate the planes of various sections through the cone, 

 published in Wieland's "American Fossil Cycads." To the right Cycado- 

 cephalus Sewardi Nathorst. Microsporangiate cone, natural size, preserved 

 as an impression on a flat slab. From a fossil-bearing bed of the Trias, at 

 Bjuf, Southern Sweden. (Left figure from Wieland, right figure from 

 Nathorst.) 



closely a plant may resemble both a cycadophyte and a fern. 

 In a sense this plant may be called a living fossil. Speci- 

 mens have since come into flower in botanic gardens, and 

 the typical cycadaceous cones (Fig. 91) leave no doubt 

 that the plant is a true cycadophyte. 



