A GENERAL SURVEY 3 



the descendants of a race which dominated the 

 world during the time when our coal deposits 

 were being formed. At this period, when the 

 horsetails grew into great trees, they were 

 represented by a large number of species. 

 Nowadays in all the world there is only a single 

 genus with, perhaps, thirty named kinds, and 

 the largest tropical sorts could hardly be called 

 trees. So far as the number of species is 

 concerned, the club mosses are much better re- 

 presented at the present time than the horse- 

 tails. Already several hundred kinds have 

 been named, and additions are frequently being 

 made. But there are no very large club mosses 

 in the world to-day. Some tropical species 

 grow into little shrubs a couple of feet high, 

 whilst a few of the rambhng examples may be 

 a score or more feet in length. These are not 

 to be compared with the giants of the coal 

 forests. Fossil remains have enabled botanists 

 to state positively that these club mosses 

 were not uncommonly one hundred feet in 

 height. 



For some reason, which it is not easy to 

 explain, the ferns, alone amongst the higher 

 flowerless plants, do not seem to have altered 



