174 THE EVOLUTION OF PLANTS 



in a plant like Miadesmia, if it was an epiphyte 

 on trees. 



All this is pure hypothesis, and is only suggested 

 because it may help us to realise that the Palaeo- 

 zoic plants were subject to a struggle for existence 

 like the plants of OUT own day, and could not 

 afford to indulge in structural elaborations unless 

 they were of real use under the conditions of their 

 fife. But it must be acknowledged that nothing 

 is more difficult than to find out why one plant 

 equips itself for the struggle with one device 

 and another attains the same end in quite a 

 different way. 



From what has been said it appears that 

 the Selaginella line has gone on from Palaeozoic 

 times with comparatively little change, except 

 that the highest types have dropped out, owing 

 perhaps to their becoming involved in keener 

 competition with other races of plants. 



We have not yet touched the main body of 

 the Palaeozoic Lycopods, the Lepidodendreae. 

 Their relations to living plants are by no means 

 so clear as in the case of the Selaginellaceae, so 

 we will not attempt in the first instance to trace 

 back their history from living forms, but will 

 first sketch the main outlines of the fossil group, 

 and will then see whether we can connect them 

 at all with any surviving type, or whether it is 



