Sex and death in the world of plants

It is only since Linnaeus published Systemma Naturae in 1735, which classified the plant kingdom by their sexual organs, that prudish religious prejudice began to be overcome — and only in the last 100 years that the sex life of plants was publicly discussed and plant breeders could utilise Darwin’s and Mendel’s work to breed new plants

That flowers were created to show the sexual organs of plants and not created for our pleasure was a shock.

As plants are unable to move like humans to affect the sexual union of the male sperm with the female egg, plants have had to be creative, with over 10 different methods to achieve the genetic offspring of seeds.

Just as the earth goes around the sun and Galileo was forced to recant what was written in the Bible, the wicked lies of plant sex behaviour have finally been excepted by the Church.

Why is sex so important?

“Because it is the chief instrument of evolution ... once sex was invented evolution became inevitable with natural selection being based on sexual selection.” - Peter Thompson

Selection is based upon variation and within every species no two sexually-produced plants or animals are exactly identical and this variation occurs by the mixing of male and female genes at each copulation. Biodiversity is our fail safe mechanism to enable us to adapt to change.

Why is death so important?

Because reproduction increases populations, it needs a mechanism to remove the obsolete ones, hence sex and death are the two sides of the coin.

Cross-pollination by insects

Lily flowers blatantly expose their sex organs to attract insects from far and wide to ensure pollination and the creation of seed. The differing heights of sexual organs in flowers like the lilum are designed to avoid self-pollination (inbreeding).

Most plants are hermaphrodites, having both male and female parts in the same flower. To extend the human analogy it would be like a Homo sapiens having a vagina and a penis on the same person. This combination would produce both eggs and semen and be self-fertilising which contradicts the taboo of incest.

Wind-pollination of corn

Corn is another hermaphrodite, like the lily, but it and all the other members of the grass family are wind-pollinated and monoecious, meaning it has separate male and female flowers on the same plant, rather than on different plants like spinach.

In corn, the male flowers are positioned above the female flowers, i.e. silks, below containing the ears (cobs). The flowers are self-compatible with pollen being spread by wind and not by insects (corn being wind-pollinated means it is subject to inbreeding depression, so seed savers need to replant at least a hundred plants for true-to-type maintenance).

Male and female parts

Unlike lily flowers which expose their sexuality, the humble spinach is the plant that is the closest to humans in its method of reproduction. Spinach plants express sex with separate male and female plants — females have egg-bearing flowers that must await the transfer of pollen (the male genes) from a separate, flowering male plant whose flowers look very different to the female.

Just as male humans look sexually different to female humans, spinach male and female flowers look different but that’s because plants can’t move like humans to copulate, being rooted in the ground, and need far more imaginative, more complex gymnastics to execute sex and the transfer of genes. In fact, male spinach plants rely on wind to transfer male sperm, i.e. plant pollen, and generates millions of dust-like grains which must land on the receptive female pistil before fertilisation occurs and seed is formed. In this case, we would classify humans as dioecious, and we share this characteristic with asparagus, date palm, paw paw, carob, persimmon and hops.

Other types of pollination

Insect Pollination

Pumpkin and zucchini. This is another sexual variation with separate male and female flowers on the same plant being self-compatible, just like corn, but relying on insects. Without insects to transfer the pollen, there would be no fruit. The first few flowers are male flowers but it is the female flowers with the swollen ovary that provide the nectar and the reward for pollination.

Self-Pollinating Tomatoes

Our favourite vegetable/fruit is also a hermaphrodite which botanists describe as having “perfect flowers”, i.e. having male and female flowers within the same flower and being self-pollinating so there is no need for cross-pollination by wind, birds or insects.
Gardeners can collect seed from tomatoes with minimum separation between plants and expect uniformity for generations to come. Lettuces, peas, French beans, rice, barley and wheat are the other self pollinating crops.

Self-Compatible Flowers

Unlike Homo sapiens, plants can change sex at will, specifically to avoid inbreeding depression or self pollination. Transvestite avocado flowers perform genital gymnastics by flowers opening as a female when males are not ready and then opening as male when female flowers are not receptive. Temperature triggers flowering and fruit failure is usually caused by planting varieties where flowering occurs when weather is too cold. This cross-pollinated plant produces a single seed which, when sown, is unlike its parents.

All Female Flowers (Hand-Pollination in Glasshouses)

Most cucumbers that we buy in supermarkets today are produced because a specific, mutated cultivar that produces only-female flowers is planted. Pollen from male cucumbers is needed but growers yields are much greater, with 100% planting of all female plants.

Moth Pollination

The Cruel Plant, which we have grown, is a lethal pinch trap. Night-flying moths are attracted to its fragrant, white flowers but the flowers face downwards, prevent landing so the moth flutters whilst inserting its long tongue up the flower tube to suck its nectar. The plant traps the moth’s tongue to affect pollination, but feeble moth perishes before the trap opens, as we have witnessed.

Self-Pollination (When All Else Fails!)

If cross-pollination is frustrated, the Cup & Saucer Vine doesn’t give up. Its stamen raises in a last ditch erection to fertilise the female part of the flower, the pistil, and self-pollinates.

The soil profile

Digging deep into the soil we often see a distinct banding of different coloured and textured material — the soil profile.

• The topsoil tends to be darker, it is where the majority of organic matter and life is found. Most root activity occurs in the top 15 cm of the soil
• The subsoil is less fertile and usually paler. There are few roots here, mainly from larger or more drought tolerant plants
• The parent material is the mineral element of the soil – weathered rock below which lies the parent rock itself