10 THE FLOWERING PROCESS 



periods which cause a profuse production of flowering hormone and 

 subsequent conversion of all buds to flowers. 



Many biennials require the cold of winter for initiation of flowers. 

 Thus they grow vegetatively the first year, producing many leaves 

 and often storing reserve food in the root or some other organ. Again, 

 if they are kept warm, some of them will grow in this manner 

 indefinitely. But following the first winter they form flowers, use up 

 their buds, and die. So-called winter annuals may germinate in the 

 fall, respond to the low temperatures of winter, and flower and die 

 the next spring soon after producing only a limited vegetative growth. 

 Another group of plants survives more than one year but finally 

 flowers once and then dies. Other mechanisms, for the most part not 

 very well understood, are involved. The "century" plant may grow 

 vegetatively for a dozen or so years and then send up a flower stalk 

 and die. It may be that formation of the flower stalk depends upon 

 storage of ample food, but other factors could also be involved 

 (accumulation of a flowering hormone which does not reach a 

 sufficiently high level for a decade or so ?). Certain bamboo plants 

 may live for up to 50 years, flower once, and then die. Perhaps in 

 such cases flowering does occur in response to the environment, but 

 the plant is not able to respond until it has reached a certain age. We 

 would say that it must reach "ripeness to flower". 



The true perennials convert only a certain portion of their buds 

 to flowers, keeping others in the vegetative condition indefinitely. 

 Often a certain age must be reached, but flowering then continues at 

 yearly intervals. The plant may produce flowers only from the 

 axillary buds and never from the primary, central shoot tip, which 

 always remains vegetative. Or the converse may be true. 



One of the most striking perennials is the so-called bottle brush tree. 

 Here the flowers form only in the axils just below the apical meristem 

 itself. The central meristem continues to grow, producing axillary 

 flowers (with long stamens, giving the bottle brush appearance) 

 during the flowering season and then finally leaves and stem again. 

 The familiar woody plants of street, garden and forest are peren- 

 nials, and yet they are the ones that have been studied the least. This 

 is probably because experimentation with them requires a great deal 

 of time, and the annuals are much easier to work with. 



At any rate it should be clear that much remains to be learned 

 about flowering. We will proceed with our survey of what is known. 



