The production of new individuals from the mother is called reproduction. Most plants have the vegetative structure of plants such as roots, stems and leaves, and the isolated larvae grow into mature bodies over a period of time. There are two ways in which plants produce offspring, asexual reproduction and sexual reproduction. Asexual reproduction plants do not need to be combined with each other by germ cells to produce larvae, and the mother can directly produce new individuals that do not change hereditary traits. Vegetative reproduction is a common asexual reproduction, without the need for seeds as larvae for propagation and propagation, the roots, stems and leaves of plants can grow independently as new larvae, such as potato tubers, bamboo rhizomes, etc. Algae can multiply rapidly using water and nutrients, and some algae can split into two or more "fragments" that grow into new individuals, a process that is repeated over and over again, covering a large area in a very short period of time. Asexual reproduction of plants can also be done through sporophyte transmission, which are germ cells that can develop into new individuals out of the plant body. Some asexual spores have a short ability to swim, others need to form a hard protective shell relying on air, water and other passive transmission, and obtain favorable living conditions, and the spores develop into new individuals. Some lower plants, algae, mosses, ferns, etc. multiply through spores.
Secondly, we are talking about sexual reproduction, flowering plants are typical of sexual reproduction, flowers are the reproductive part of plants, and the stamens in the flowers are male reproductive organs, and pistils are female reproductive organs. Some flowers contain only a single stamen or pistil, while others contain both stamens and pistils, which contain both male and female gametes. In sexual reproduction of plants, two gametes combine to form zygotes under pollination, and animals are fertilized. The ovary of the flower then grows into a fruit, the other parts fall off, and the ovules develop into seeds, which contain a wrapped embryo. Some fruits are delicious and juicy, such as mangoes and oranges, and some are hard, such as almonds and walnuts.
The way plants reproduce by both sexes actually comes at a cost because it destroys the good genes that already survive in the environment. This is a universal cost of recombination, and the cost of adaptation is that recombination has a higher mutation efficiency, resulting in the small evolution that we are familiar with, and the gradual accumulation of small evolutionary pressure can produce large enough characteristic differences [1], natural adaptation efficiency stratification, evolutionary razor can complete the screening of efficiency. The sexual process is important for the persistence of a species, it makes the population more diverse, and all organisms are different. If environmental conditions change, only adaptation can survive and continue to reproduce to expand population survival boundaries to occupy the newly changed environmental conditions, which prevents the transfer of deadly mutations to offspring, because those mutated organisms have died.
So, plants have no legs, how to achieve the spread of spores or seeds to expand the survival boundaries of the population?
In nature, the same plant can grow in different places because the seeds are dispersed to different places. Sometimes after walking through a forest, field, or park, you may find seeds or fruits sticking to your clothes. Plants benefit from the spread of seeds or spores, and everything in nature that can move can become a carrier of transmission, flowing water, blowing wind, animals constantly looking for food, and so on. To this end, seeds have evolved structures suitable for propagation, such as sunflower and dandelion seeds with the help of the wind, coconuts form spongy fruits with floating ability, some of which are carried elsewhere through the thorny surface of the seeds adhering to the animals, and can also be compensated for the spread of seeds by providing food that the animals can eat. Interestingly, the last mode of transmission, plants provide animal food, while animals achieve the spread of seeds in food, and the reproductive boundaries of plants are coordinated with the development of animal survival boundaries. If all the seeds of a plant are concentrated in one place, then the competition for sunlight, water, minerals and space will be very fierce, these seeds will not all mature, more spreadable seeds and breeding plants have higher reproductive efficiency, and the population can invade new habitats to explore new habitats during a period of natural environmental change, achieving a wider distribution and survival.
Different parts of the plant are modified to disperse and spread, and the fruit, part of the fruit or other structure, or even the whole plant, may be involved in the spread. Plants need to use abiotic forces to complete the transmission, but also need the help of animals, ants are often involved in the transmission, birds, mammals, reptiles, fish are effective carriers of transmission. Animal transmission may be passive, plants evolve to mangs, hooks, barbs, or mucus, or it may be active, birds and squirrels will take seeds elsewhere for storage and then eat them, ants will store some seeds, and other animals will eat fruit and excrete seeds through feces to new territories.[2] The dispersal method is related to the plants in the habitat, grasslands, mountains, and weedy areas of the forest typically rely on wind to spread, while forest plants that grow lower off the ground need to rely on animals for transmission, and plants in wet areas use water for transmission.
At the same time, plants do not have eyes, noses, ears and other organs that collect information about the characteristics of external things, how do male gametes in sexual reproduction efficiently find female gametes?
Plants may not be as free as animals in their "monogamous" mode of operation, and when reptiles collect mate features through information organs such as vision to actively approach and complete mating, plants cannot do this because their tissues and organs are completely different from the evolutionary purposes of animals. Ferns replace the active mating of animals with spore "carpet bombardment", and the passive spread of hundreds of millions of spores increases the chance that the two spores will be close to each other, with the minimum distance between sperm and egg cells. However, simply increasing the number of spores is a huge waste of resources, and plants will minimize the size of the spores, which will also allow for longer dispersal distances. As a result, plants eventually "divide labor" and are able to produce large numbers of tiny male spores to develop into male gametosites and a small number of larger female spores of female gametophytes [1].
Most of the seed plants are angiosperms, many have a torso high above the ground, how do male and female gametes find each other? The only possible solution is flowering and pollination. The sperm in the pollen grain will swim from the liquid on the top of the ovules into the egg cells, and the more advanced way is the sperm delivery. These ways of breeding seed plants allow them to survive in drier places, transforming the environment while also giving other life a foothold. Pollination requires the help of third-party forces, and it is easy to think of external forces such as wind disturbing plants, but this is a clumsy way of pollination, and plants need to produce excess pollen without any accuracy. Secondly, insects (butterflies, bees, etc.), birds, etc. can carry pollen to pollinate in some cases. Flowering angiosperms have a high growth efficiency and can be easily copied from other parts of the body when eaten, and many flowers can adapt to insect pollination and tempt animals with delicious fruits for seed distribution. Today they dominate the plant kingdom of the earth, with as many as 250,000 species, more than any creature except insects.
[1] Alexey Shipunov，Introduction to Botany,2020,第113-114页
[1] STEPHEN C. STEARNS，The evolutionary maintenance of sexual reproduction: The solutions proposed for a longstanding problem，J. Genet. Vol. 69, No. 1, April 1990, pp. 1-10。
[2] Kenneth R. Robertson, Stephen R. Downie, Sandra L. Mason, Botany，2006，第40-41页。