80 GENERAL BOTANY 



Now one may often see a plant twining round the 

 stem of a tree, and looking as if it had cut into the 

 bark. This is because the tree has gone on growing 

 in thickness except where actually prevented by the 

 coils. But you never see this on a Palm. For in- 

 stance one sometimes sees a FICUS or Banyan 

 growing on a Palmyra and sending its roots round the 

 stem, having started from seed left by some bird in 

 he axil of an old leaf-base. But it never has the 

 appearance of cutting into the palm, simply because 

 the latter has not increased at all in thickness. 



It is probably because of their inability to grow in 

 thickness that, with the exception of Palms, all mono- 

 cotyledons are comparatively small plants, and do not 

 have branches except near the ground. Even Palms, 

 tall as they may be, have comparatively thin stems, 

 and are very rarely branched. 



Formerly it was supposed that Palms and other 

 monocotyledons did grow a little in thickness by the 

 addition of new woody matter inside the old, and 

 they were therefore called Endogens (or inside growers) 

 while dicotyledons were called Exogens (outside 

 growers). These names, though still used by some 

 people, and in old botany books, have now no scientific 

 value. 



Dicotyledons on the other hand may attain almost 

 any thickness. There used to be a Chestnut-tree 

 on Mount Etna, 180 feet in circumference ; and BOMBAX 

 MALABARICUM, the silk-cotton tree, has been known 

 to attain an even greater thickness, and another very 

 thick tree the Baobab (ADANSONIA DIGITATA) is often 

 found in gardens, with trunks ten feet or more thick. 



