Apical dominance refers to the tendency of some plants to have a growing tip that inhibits the growth of laterals from the stem with the growing tip.  Here is a reference to a more in-depth article:

http://www.answers.com/topic/apical-dominance

Stopping refers to the practice of pruning buds and laterals to get larger blooms at a target time for showing purposes.  There is an article in the September 2010 Bulletin of the American Dahlia Society.  That article provides a reference to a paper published in 1984 here:

http://www.ojaste.com/docs/Stopping%20Dahlias.pdf

Source: Luther Burbank - His Methods and Discoveries and Their Practical Application, Chapter VII, Volume IX, Luther Burbank Press, Copyright MCMXIV.

An Infinity of Variation Which Has Only Been Tapped

If you have seen a Navajo blanket you are aware that the Indians of the Southwest are lovers of vivd colors - in particular of glaring reds.

It would appear that the insects of the same region have acquired similar tastes; for they have aided in the development of a good many flowers that advertise their wares with the most brilliant hues.  The cactus furnishes a familiar instance.

Another example is supplied by the even more familiar dahlia, which in its native Mexican form had florets of bright red with a yellow center - supplying the basis for the modified color schemes of the dahlias now under cultivation everywhere.

The original red dahlia so attracted the eyes of the Spanish conquerors in Mexico that they sent the plant to Europe, and its reception there suggests that barbarian and insect have no monopoly of the color sense to which red appeals.  For the Mexican composite flower was taken into the European gardens, and made to feel quite at home in its new habitat.

The new exotic came, as a matter of course, under the eye of the great classifier Linnaeus.  And he thought so highly of it that he was moved to name it in honor of his friend and pupil, Dr. Andreas Dahl.  The great Swedish classifier spoke with final authority in that day, and "Dahlia" the plant became in all languages and wherever grown - except, of course, in its native habitat; and what it might be called there, if anything, did not greatly concern the civilized world.