Flowering in Woody Plants • 121 



cedures traditionally used in the hope of hastening flowering has 

 only recently been confirmed in controlled experiments, and the 

 value of some others is still uncertain. 



Further problems are presented by the fact that most trees and 

 shrubs, at least in the temperate zone, are probably indirect- 

 flowering plants unlike most herbs studied, so that conditions 

 required for flower initiation may differ greatly from those favoring 

 flower development, and the internal changes involved may differ 

 as well. As an extreme example, the difficulties faced by the forest 

 geneticist are evident in the fact that not only must most species 

 of pine (Piniis) grow for some five or more years before flower 

 initiation is possible, but then two and a half years are required 

 to obtain seed. Flower primordia are formed in the spring of one 

 year but do not develop further until the spring of the next, when 

 pollination takes place. Then in the succeeding spring and summer 

 cone elongation and actual fertilization finally occur, following 

 which the seeds mature in the fall (see Stanley, 1958). Clearly, any 

 way of reducing the age required for flowering and speeding up the 

 reproductive cycle itself would be extremely helpful. 



A particular group of woody plants, the bamboos (Tribe 

 Bambuseae of the grass family), provides the most striking exam- 

 ples of long-lived monocarpic plants (Chapter One), which flower 

 once and then die. As summarized by Arber (1934), there is abun- 

 dant evidence that a bamboo will spend 5 to 50 years, the number 

 being characteristic of the species, in vigorous vegetative growth. 

 It then flowers, sets seed, and dies within a short time. Usually all 

 plants of the species within a large area will flower at the same 

 time, regardless of injury or even of destruction of all portions 

 above ground by cutting or fire. Thus size alone does not appear 

 to be a factor. Individuals transplanted to, say, the Kew Botanical 

 Gardens still flower the same year as their fellows in the tropics, 

 making it seem unlikely that periodic environmental changes such 

 as droughts are the cause of such behavior— although this has been 

 suggested. Possibly bamboos may provide instances of very long- 

 term endogenous rhythms, but it will take a long-lived plant 

 physiologist or a well-endowed research institute to find out. 

 Certainly in no group of plants is the relation between age and 

 flowering more evident and less understood. 



Most environmental factors affecting flowering in trees have 



