Flowering in Woody Plants • 123 



verrucosa, normally requiring at least 5 years from seed in order 

 to flower, was used by Longman and Wareing (1959) in a study on 

 whether size was the major factor involved or whether a certain 

 number of developmental seasonal "cycles" were necessary before 

 flowering could take place. Some seedlings were kept constantly 

 under long days or continuous light, in which vegetative growth 

 continues rapidly. Others were allowed to make about 30 centi- 

 meters of growth under such conditions, given short days to induce 

 dormancy, and then kept in the cold for six weeks, following which 

 they were returned to long days and the cycle repeated. There was 

 also a control series under natural conditions. Fifty percent of the 

 trees in the constant long-day conditions flowered within the first 

 year, when 2 to 3 meters high, whereas none of the (smaller) control 

 or "cycle" series flowered within two years. Hence in this tree at 

 least, attainment of a certain size is crucial to flowering and can be 

 speeded by constant long photoperiods, although the authors noted 

 that the plants so treated were abnormally spindly. 



Although flowering may thus be hastened by speeding devel- 

 opment to the requisite size, most of the traditional methods used 

 by horticulturists involve operations or mutilations of some kind 

 and bring about an inhibition of vegetative growth. Of these 

 methods, one of the most widely favored is girdling— the removal 

 of a ring of bark, including phloem, on an entire tree or on a 

 branch. The immediate result is to prevent the translocation of 

 photosynthate out of the girdled top or branch, so that materials, 

 accumulate above the girdle. Naturally, this can thus result in the 

 death by starvation of the root system if it is not permitted to heal 

 over within a relatively short time. Girdling is often effective in 

 causing flowering of plants too young to flower otherwise in species, 

 as unrelated as Citrus (Furr et al., 1947), Pin us (Hoekstra and 

 Mergen, 1957), and apples (Sax, 1957, 1958b). Related to girdling 

 as a means of blocking phloem translocation is the technique of 

 bark inversion, in which a ring ol, bark is cut out and regrafted 

 in place upside down. Such procedures must be used before the 

 period in which flower initiation would normally be expected to 

 take place. In apples, bark inversion in June will affect flowering 

 the following spring, even bringing it about in 2- or 3-year-old 

 seedlings, whereas the same operation in late summer is ineffective 

 (Sax, 1957, 1958b). 



