50 DIMORPHIC BEANCHES IN TROPICAL CROP PLANTS. 



dormant. They do not appear to be present on young plants, and 

 they are never added after the internode and its leaf or leaves have 

 become mature. They are laid down with regularity as a part of each 

 internode of the adult plant. 



The extra-axillary buds, both in cotton and coffee, are developed 

 with the same invariable regularity as the leaves themselves. They 

 resemble adventitious buds only in the technical sense that their posi- 

 tion is extra-axillary. Considered from the standpoint of the habit 

 and functions of the plant, they are not more adventitious than the 

 terminal or the axillary buds. 



Before the young internode emerges from between the stipules of 

 the coffee leaves, the three buds that give rise to the central axis and 

 the two lateral branches can be found standing in a row with the axil- 

 lary buds and only very slightly above them. Later on the three 

 buds are pushed out nearly together, but the middle one soon leaves 

 the other two behind. Strictly speaking, therefore, the extra-axillary 

 branches of coffee arise from subterminal buds. After the branches 

 are formed there is no internal indication of a joint or septum; the 

 pith is quite continuous. Thus an internode of a main stem or an 

 upright branch of coffee does not appear to be a simple cylinder, but a 

 three-armed fork or trident. 



The lateral branches of the coffee plant do not normally branch 

 again, though they can be forced to do so by pruning. The secondary 

 lateral branches are produced from sterilized flower buds, and have 

 only the characters of laterals, never of uprights. Persistent pruning 

 may exhaust all the buds capable of forming uprights and leave the 

 tree a tangle of horizontal or drooping branches, apparently without 

 the power to put forth any more uprights. 



Branches of definitely limited possibilities of vegetative growth, 

 like the fruiting branches of coffee and Castilla, may be considered as 

 having intermediate functions between those of leaves and of or- 

 dinary types of vegetative branches. The leaves of Begonia and 

 Bryophyllum, which produce plantlets from adventitious buds, and 

 the leaf-like flower-bearing organs of Phyllanthus and Phyllonoma 

 represent other intermediate stages between ordinary leaves and 

 branches. The leaf-like branch organs of some of the relatives of 

 asparagus, such as Ruscus and Semele, might be mentioned in the 

 same connection. Even the tobacco leaf may develop a roAv of vege- 

 tative buds along the base of the midrib. The axillaiy branches of 

 Castilla are as definitely deciduous as the leaves. The permanent 

 branches of coffee are formed from axillary buds, while those of Cas- 

 tilla appear to be adventitious as regards the time of development, 

 though they have definite positions. 



Unless the different branch organs are to receive distinctive names 

 in each of the different plants, it will be necessary to content our- 



198 



