PAST HISTORIES OF PLANT FAMILIES 113 



sperms, which swim towards the female cell in the space 

 provided for them in the seed (see p.c, fig. 76). 



The characters of the Cycads as they are now 

 living prove them to be an extremely primitive group, 

 and therefore presumably well represented among the 

 fossils; and indeed among the Mesozoic rocks there is 

 no lack of impressions which have been described as the 

 leaves of Cycads. There is, however, very little reliable 

 material, and practically none which shows good micro- 

 scopic structure. Leaf impressions alone are most un- 

 safe — more unsafe in this group, perhaps, than in any 

 other — for reasons that will be apparent later on, and 

 the conclusions that used to be drawn about the vast 

 number of Cycads which inhabited the globe in the early 

 Mesozoic must be looked on with caution, resulting from 

 the experience of recent discoveries proving many of 

 these leaves to belong to a different family. 



There remain, however, many authentic specimens 

 which show that Cycas certainly goes back very far in 

 history, and specimens of this genus are known from 

 the older Mesozoic rocks. We cannot say, however, as 

 securely as used to be said, that the Mesozoic was the 

 " Age of Cycads ", although it was doubtless the age of 

 plants which had much of the external appearance of 

 Cycads. 



From the Palaeozoic we have no reliable evidence of 

 the existence of Cycads, though the plants of that time 

 included a group which has an undoubted connection 

 with them. 



Indeed, so far as fossil evidence goes, we must sup- 

 pose that the Cycads, since their appearance, possibly at 

 the close of the Palaeozoic, have never been a dominant 

 or very extensive family, though they grew in the past 

 all over the world, and in Europe seem to have remained 

 till the middle of the Tertiary epoch. 



(0122) ^"^ 



