Flowering stimulus

Perhaps the critical stimulus perceived by the plant is an increase in the length of the night per se, an hypothesis that could easily be tested. Flowering plants have been collected from near Cerro Quemado in March, and local villagers insisted S. divinorum flowers most abundantly in March, April, and May, when it is the driest. In light of the conditions that promote flowering during the cool and wet winter, these assertions seem more than reasonable. 

Still another factor in spacing conununication system stability is residual activity of a chemical stimulus, which may vary over time according to the insect species and the nature of the message conveyed. For example, the repellent pheromone deposited by Xylocopa bees following extraction of nectar from passion flowers persists for only about 10 minutes, which may coincide with the time required for replenishment of some of the nectar, whereas Oecophylla ants deposit territorial pheromone which persists for up to 12 days, designating areas of continuous exploitation (see Section 11.5). Residual activity... 

The floral stimulus acts at the apex and therefore determination of the site of GA action is important in formulating logical hypotheses about the role of GAs in flower initiation. Although not examined in many species, the evidence indicates that GAs can affect flower initiation at different sites. Flower induction brought about by GAg treatments in Bryophyllum daigremontianum and Hyoscyamus niger is the result of GA action in the leaves, not the apex where the floral stimulus acts [21, 22]. The situation is quite different in the SDP Pharbitis nil and Impatiens balsamina, where it was determined that the apex is the site of GA action [ 16,25,27]. 

Grafting experiments with two inbred lines of Silene armeria that differ in their sensitivities to GA3 demonstrate that the above results are not unique. In one line, application of G A3 in SD induces both flower initiation and stem elongation, while in the other ( GA" line), only bolting is observed. However, flowering of the GA" line under SD can be obtained when grafted onto donor stocks of the GA sensitive line that had been induced with GA3 [20]. Again, it is difficult to see how GA3 and the floral stimulus could be identical. 

However, when applied to plants kept strictly vegetative by continuous growth in SD, BA was unable to cause flower initiation, even when the treatment was repeated [4]. However, a single low-dose application in SD, timed to correspond with the time of movement of the mitotic stimulus in LD-induced plants, caused an early mitotic activation in the meristem [4]. Interestingly, the timing, magnitude and characteristics of this activation were the same as in meristems of LD-induced... 

A disadvantage of increased secondary product production in response to ethephon was reported by Arita et al. [2], who showed that the Chinese rose bettle (Adoretus sinicus Burmeister) fed preferentially on leaves of ginger plants that had been treated with ethephon. The feeding stimulus was not ethylene itself, but presumably a volatile produced by the plant in response to the ethephon treatment. An interesting use of ethephon for insect control is its late-season use during cotton production to remove squares (young flowers), and reduce the opportunity for insects to overwinter [25]. This treatment reduced the number of infested bolls and squares to less than 5% of those in the control plots. 

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