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# 5. Proof by experiment

Since this is science, we decided that the best way to try harder, to correct misunderstandings, and to present our ideas was with some data. We therefore took up our chosen test species, the well-known semelparous organism Brassica rapa. We planted four seeds in several pots, each of standard size. Pot dimensions were 1.8 cm x 1.8 cm x 5.7 cm, giving a capacity of 18.5 cm3 each. We maintained uniform growing conditions, providing a constant and controlled 24-hr light source, and a continuous water supply.

We carefully measured both the mass and the energy of the plants at a variety of stages, equally carefully noting dates. Not all seeds grew and/or survived, and we were particularly careful to note survivor numbers at each stage, so we could determine all relevant rates of growth and change.

Once our first generation had developed true leaves, we selected five random pots for destructive harvesting and measurement. We allowed all other, non-destroyed, pots to continue to the next stage. We could only take one measure for root mass per each pot. The root web complex the plants produced was so entangled that it was not possible to determine which rootlets, and root-sets, truly belonged to which plant. We therefore averaged root mass data over all survivor plants in any given pot.

We also carefully measured all plants, within each pot, for leaf area, leaf mass, and stem mass. We measured photosynthesis per unit leaf area. However, because of the delicacy of the measurements, and the amount of time they took, we only measured photosynthesis data for a maximum of three plants in each pot, again averaging out that data over all plants in that pot. We then applied our pot average rate per unit leaf area to all plants within that pot to allocate a photosynthetic rate for each specific plant in that pot.

We hand-pollinated each generation at least twice so the plants could set seed. We placed dried bees on toothpicks and rubbed them across the anthers to pick up pollen, which we then applied to the stigmas to effect a transfer.

We repeated the above harvesting, destruction, and measurement regimen at the flowering, fruiting, and mature fruit stages, again selecting five pots at random, carefully noting dates and survivor numbers. We also measured, in the later stages, both the total biomass and the total energy of all flowers and fruits present. Since the plants were drying and senescing as a part of their natural cycle, we could only measure biomass in the final stage. We could not measure photosynthesis. After the plants had senesced, fruits were harvested and their seeds counted.

Plant biomass is approximately 45% carbon and there are approximately 8.08 cal/g of carbon in plant tissue—equivalent to 1929.78 joules per gram (we used joules in all calculations). We measured photosynthesis in units of carbon gained per unit leaf area per second. We used biomass to infer plant energy content.

Our first generation of plants, which we planted at a density of four seeds per each pot, produced an average of ten seeds per pot. We therefore planted ten seeds per pot to produce a second generation and repeated the entire above measurement and destruction process. Our second generation produced an average of fourteen seeds per pot, and we therefore planted fourteen seeds per pot to produce our third generation. Due to the stress responses placed upon this third generation, it was not possible to take photosynthesis measurements at their fruiting stage.

Since the third generation only produced five seeds per pot and our Brassica rapa population had therefore collapsed back to its initial levels, we collated all measurements for biomass, energy content, photosynthesis rates, and numbers and calculated the species’ equilibrium age distribution population. Values are given in Table 1.

For ease, and for an immediacy of comprehension, population numbers have been scaled up and expressed such that the average number over the Brassica rapa generation is 1,000 entities … which we are calling “one biomole”. The data in Table 1 is therefore expressed in our biomoles.

Stage |
Av. indiv. mass, m̅ |
Av. indiv. energy, h̅ |
Energy Flux, µ |
Time |
N, in biomoles |
---|---|---|---|---|---|

Seed |
1.171 x 10-3 grams/sec |
1.017 joules |
3.276 x 10-05 watts |
0 days |
1.096 [x 103] |

Leaf |
4.977 x 10-2 grams/sec |
7.021 joules |
4.151 x 10-04 watts |
6 days |
0.767 [x 103] |

Flowering |
6.503 x 10-2 grams/sec |
15.232 joules |
1.949 x 10-4 watts |
9 days |
0.724 [x 103] |

Fruit |
8.717 x 10-2 grams/sec |
13.959 joules |
1.124 x 10-04 watts |
18 days |
0.662 [x 103] |

Dry seed |
1.049 x 10-1 grams/sec |
15.558 joules |
0 watts |
32 days |
1.751 [x 103] |

Seed |
1.171 x 10-3 grams/sec |
1.017 joules |
3.276 x 10-05 watts |
36 days |
1.096 [x 103] |