FLOWERING IN ITS BIOLOGICAL FRAMEWORK 9 



process from this standpoint becomes of extremely broad and 

 fundamental significance. 



The disappointing thing is that we know little more about the 

 topic than has already been stated above. The problem will be 

 mentioned again in the last chapter along with a summary of what 

 has been done so far to try to solve it, but at this stage very little 

 is known. 



The initiation of flowers is a change-over from the indeterminate 

 to the determinate form of growth. The indeterminate form of 

 growth of a plant stem confers potential immortality to the vegetative 

 plant. Leaves, stems and branches can be produced indefinitely, so 

 long as the apical meristem remains alive and active. Thus cuttings 

 might well be taken from the 4000-year-old pine trees in the Sierra 

 Mountains of California, and these might grow for another 4000 

 years, after which other cuttings could be taken, and so on potentially 

 forever. 



The determinate form of growth, typical of most animals, leads 

 to death. The embryo grows, essentially in all directions, until 

 maturity is reached, senescence finally sets in, and death ends the 

 process. Preservation of the species depends upon starting over, so 

 to speak, as single cells from male and female are combined to 

 produce the zygote and new individual. 



The flower and subsequent fruit also have the determinate growth 

 form. In a sense, the vegetative meristem is "used up" when it 

 develops into the flower. It is no longer capable of producing the 

 plant body as a whole, but only the determinate flower parts — and 

 of course the gametes which may form the zygote and new individual 

 plant. Thus the initiation of sex organs exchanges the potential of 

 immortality for the possibility of combining germ plasm to produce 

 a new individual. Might we thus conclude that sex leads to death? 



The flowering plants have solved the problem in various ways. 

 The true annuals have made the sacrifice. If in nature the environ- 

 ment (or their own internal metabolism) causes them to convert all 

 their buds to flowers during their first year of life, then they only live 

 one year, preserving the species until the next year only in the form 

 of the seed. The cocklebur is an excellent example. It will live for 

 years (potentially forever) in a greenhouse with artificial light where 

 it never is exposed to a dark period exceeding 8^ hr. It can be killed 

 within 2 months, however, by exposing it to a number of long dark 



