78 THE EVOLUTION OF PLANTS 



of Cycadophyta, of which only the one family, 

 Cycadaceae, has come down to our own times. 



The Cycadophytes of the Mesozoic had a 

 world-wide distribution, extending from the trop- 

 ics all through the temperate zones into the Arc- 

 tic regions of Greenland and Siberia, and the 

 Antarctic of Louis Philippe Land. 



They were abundant hi our own country and 

 their stems are familiar objects in the quarries 

 of Portland, where they are called " Crows' 

 Nests " by the workmen. The vegetation of the 

 world in those days was astonishingly uniform; 

 quite similar forms of Cycadophyta have been 

 found in Yorkshire, Mexico, India, and even in 

 regions where only the hardiest Arctic vegetation 

 can grow at all in these days. 



The living Cycads, as we have seen, are appar- 

 ently a simple group of Flowering Plants; they 

 show, in various features, especially in their mode 

 of fertilisation, in the arrangement of their pollen- 

 sacs, and hi the carpels of Cycas, a decided ap- 

 proach to Cryptogams. Among the Mesozoic 

 Cycadophytes it is rare to meet with such simple 

 forms. In a few cases fructifications similar to 

 those of recent Cycadacese have been found; in 

 particular, the genus Cycas has been recognised, by 

 means of its characteristic carpels, as far back as 

 the Lias. Leaves closely resembling those of re- 

 cent genera such as Cycas, Zamia and Dioon are 



