16 DIMORPHIC BRANCHES IN TROPICAL CROP PLANTS. 



an}' vegetative branches, though extra-axillary limbs and even axil- 

 lary limbs may be formed bj^ the same varieties when grown under 

 conditions that favor a large development of the vegetative parts. 



In the so-called " cluster " cottons it often happens that one or 

 more buds, or bolls, appear to be borne on short axillary branches, but 

 careful examination will usually show that the fruit does not come 

 directly from the axillary branch itself, but belongs to a very short 

 fertile branch arising from the axillary. In the Egyptian cotton a 

 short fertile branch is often pushed out from one side of the dormant 

 bud that represents an undeveloped axillary branch. Sometimes the 

 bud that represents an undeveloped axillary branch is carried up a 

 little on the base of the extra-axillary branch. After this has oc- 

 curred, a branch that arises from the axillary bud appears to be borne 

 by the extra-axillary branch rather than by the main stem of the 

 plant. This impression may be strengthened still further if the 

 axillary bud or the fruiting branch to which it sometimes gives rise 

 be changed into flower bud, as in the cluster cottons that show an 

 abnormal propensity toward fruit production. Sometimes the nor- 

 mal extra-axillary fruiting branch is also replaced by a single flower 

 bud, so that three flower buds may appear to come from each of the 

 nodes of the main stem instead of the more normal complement of a 

 limb and a fertile branch. 



In varieties of cotton that are not inclined to produce true axil- 

 lary limbs, the extra-axillary branches usually assume the func- 

 tions of limbs; that is, they produce flowering branches instead of 

 bearing the flowers themselves. A true axillary limb seldom stands 

 alone on the main stem, but is almost invariably accompanied or pre- 

 ceded by a fertile branch. The insertion of a limb and a branch close 

 together, at the same node, makes it easy to ascertain whether true 

 primary limbs are present or limbs that represent fruiting branches 

 transformed for vegetative purposes. 



The leaves of the vegetative limbs and those of the main stem are 

 larger and have relatively longer petioles than those of the fruiting 

 branches. Another definite difference between the leaves of the main 

 stem and those of the fertile branches, has been noticed by Mr. Row- 

 land M. Meade in the Triumph variety of Upland cotton. The 

 leaves of the main stem have nectaries on three of the veins, while 

 those of the fertile branches have only the one nectary, on the back 

 of the midrib. When the fruiting branches are shortened, as often 

 happens in the Egyptian cotton, the petioles of their leaves are also 

 greatly reduced in length, a step toward the still more distinctly ab- 

 normal condition where the leaves of tlie shortened fertile branches 

 begin to show some of the characteristics of the involucral bracts. 



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