32 



DIMOEPHIC BEANCHES IN TEOPICAL CEOF PLANTS. 



naked section at the base after the successive crops of leaves and 

 fruits have fallen. Finally the weight of the branch becomes too 

 great for the support, the soft basal joint gives way, and the branch 

 drops to the ground. The base of the branch is conical or rounded, 

 and fits into a socket in the wood of the trunk. Both the base and 

 the socket are marked with very fine radiating ridges and grooves, 

 showing that the self-pruning habit of the tree is the result of a defi- 

 nite specialization of tissues and not a mere breaking or rotting away. 

 In fact, the branch is usually still alive when it falls, and milk flows 

 out of the tree into the exposed socket to cover the wound. The bark 

 also soon grows over it and heals completely, leaving only a faint, 



rounded scar. 



The upright or permanent 



branches of Castilla are com- 



•V I _.--' ^j paratively few in number. 



They arise, one in a place, at 

 the right or the left of the base 

 of a temj^prary branch, with 

 the same regularity as in a 

 stalk of cotton. They take a 

 much more oblique or upright 

 direction than the temporary 

 or fruiting branches, which 

 / /' ■ \ are usually nearly horizontal 



or somewhat drooping. The 

 trees often grow to a height of 

 15 or 20 feet before any of 

 the permanent branches de- 

 velop, and then they often ap- 

 pear singly or a few at a time. 

 (SeefigU.) 



The idea that extra-axillary 

 buds are abnormal or excep- 

 tional appears to be quite as unwarranted in Castilla as in cotton. It 

 Avould be possible for a Castilla tree to grow to seed-bearing maturity 

 without producing any extra-axillary branches, but there would be 

 formed in this way only a simple upright stalk or trunk. All of the 

 branches that form the true permanent framework of the tree arise 

 from extra-axillary buds that might be considered adventitious. 

 AVhether such buds are added after the formation of the internodes 

 that bear them or are formed with the internodes and remain dormant 

 at first is not certain. A permanent branch is often put forth at the 

 base of a temporary branch that is still very young, in trees of suffi- 

 cient age. That permanent branches of Castilla can arise as truly 



198 



/ 



Fig. 4. — Diagram of a rubber tree with one 

 permanent vegetative branch and numerous 

 temporary fruiting branches. 



