beginner ’ s corner
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THE KEY to gene exchange between multicellular individuals is haploid sex cells , each with just half the adult DNA .”
Today , we delight in thousands of varieties of flowery sex organs , shining in the sun or shade . And we realize flowers exist almost entirely to attract bees , butterflies , wasps , flies , beetles , moths , bats , monkeys , lemurs , possums , rodents , hummingbirds , and others . Pollinators respond to aroma , color , patterns , and sweet nectar . To discourage nectar robbers such as ants , flowers create traps , clever protective structures , and diversionary tactics . It ’ s all about getting genes together , and those tantalizing blossoms use some unlikely tactics . Charles Darwin was fascinated with the co-evolution of plants and their insect pollinators . In some cases , a single species of plant and a single species of insect are totally dependent on each other for successful reproduction . Three species of moth are the only pollinators of yuccas . And yucca moths can only lay eggs in a ripe yucca flower , where larvae hatch and feed entirely on that flower . Fig species each have their own species of wasp for pollination , while the wasps lay eggs only in their special figs .
DIOECIOUS AND MONOECIOUS SEX
About six per cent of more than 250,000 flowering plant species are dioecious ( Di = “ two ,” Oikos = “ house ,” in Greek ).
Staminate ( male ) and carpellate ( female ) flowers are found on different plants . Having separate sexes prevents selffertilization , assuring cross-pollination . Seven per cent of flowering plant ( angiosperm ) genera contain some dioecious species . Familiar examples of dioecious plants include hops , date palm , yew , hemp , bay laurel , willow , African teak , holly , gingko , and common nettle . Obviously , they are all over the evolutionary map and in many unrelated families . Some dioecious plants change sex over time , usually making male flowers earlier in the season and female flowers later . Many flowering plants are monoecious (“ one house ”). They use either self-fertilizatoin ( allogamy ) or cross-pollination ( xenogamy ). About 7 per cent of higher plant species are partially cross-fertilizing and partially self-fertilizing . In monoecious plants , male stamens with pollen and female pistils are borne on the same plant , though some have separate male and female flowers . In a so-called “ perfect ” flower , each bloom has both stamens and pistils .
90 grow cycle