18 DIMOEPHIC BRANCHES IN TEOPICAL CEOP PLANTS. 



The Hindi cotton that figures in literature as a contamination of 

 the high-grade Egyptian stocks shows the slightest differentiation 

 of the fruiting branches. These branches have a curious zigzag form 

 that readily distinguishes them from the straight vegetative limbs, but 

 they may retain the nearly upright position of the limbs and do not 

 appear to have lost any of the vegetative functions. In such cases 

 the flower buds are usually aborted at an early stage, though mature 

 bolls are sometimes found on branches that remain more upright 

 and limblike than those in Upland or Egyptian varieties. 



The other extremes of differentiation in the direction of the shorten- 

 ing of the fruiting branches are found in great variety among the 

 so-called " cluster " cottons. The simplest form of clustering is rep- 

 resented by a mere shortening of the joints of the fruiting branches, 

 which brings the flowers and bolls closer together than in normal 

 long-branched varieties. More pronounced clustering leads to denser 

 groupings of bolls by the development of additional flowers on short 

 branches from the axils of the leaves of the fruiting branches. In its 

 most extreme form the clustering has the effect of reducing the num- 

 ber of bolls. The leaf buds that normally continue the growth of the 

 branches are sometimes replaced by flower buds, or adjacent leaf 

 buds may be aborted and fall off, so that the branch soon ends with 

 a flower or a boll and no more joints can be added. 



It usually appears that the cluster habit is merely a form of spe- 

 cialization of the fruiting branches, for the vegetative limbs and 

 axillary branches are usually not aft'ected at all by the cluster ten- 

 dency. In other cases the axillary buds of the vegetative branches, 

 as well as the terminal buds, may appear to be replaced by flower 

 buds, though it is usually found, on closer examination, that the 

 flower bud is borne on a short fertile branch that rises from an other- 

 wise abortive axillary branch. 



Finally, it sometimes happens, as in the Triumph variety of Upland 

 cotton, that two forms of fruiting branches are regularly produced. 

 The normal condition with the Triumph cotton is to have several of 

 the lower fruiting branches very short and determinate, so that some- 

 times this variety is erroneously described as a cluster type. 



STERILITY OK 1XTER3IEDIATE FORMS OF BRANCHES. 



Botanists are familiar Avith the fact that changes and substitution 

 of form often occur among the floral organs of plants. The most 

 familiar change of this kind is in the so-called doubling of flowers, 

 meaning the addition of a larger number of petals to the corolla. 

 In many cases the number of stamens decreases as the petals become 

 more numerous, and many double flowers are completely sterile, both 

 the stamens and pistils being transformed into petal-like organs. 



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