A Closer Look at Plant Reproduction, Growth, and Ecology
A CLOSER LOOK AT PLANT REPRODUCTION Grow TH AND ECOLOGY Many garden plants reproduce more effi ciently from roots stems and leaves than from seeds which are a part of sexual repro duction Such vegetative reproduction has the advantage of producing larger plants more rapidly The potato seed for example is very small and develops into a small weak plant The potato itself though is actually a tuber a fleshy underground stem that contains a reserve supply of starch and pro duces a strong fast growing plant Vegetative reproduction enables plants to spread quickly over the area surrounding the parent plant Many weeds are difficult to control because they grow quickly using vegetative repro duction In addition to runners and tubers bulbs underground buds corms vertical underground stems and rhizomes horizon tal underground stems are other parts from which new plants may grow Cuttings also called slips are twigs branches or leaves cut from the parent plant and placed in soil sand or water In time new roots stems and leaves grow from the cuttings The willow tree geranium begonia and African violet are examples of plants that may be produced in this way A process called layering is used with certain trees and shrubs When a branch is bent down to touch the 12
METHODs OF PLANT REPRODUCTION soil it sends roots into the ground and a new plant results Gooseberries blackberries grapevines and forsythia may be reproduced in this way Improved varieties of fruit are obtained by grafting In this process the stem of a plant that has produced superior fruit is made to grow on the stem of another plant called the stock of hardy but inferior quality The stems are cut so that the cambium lay ers a type of growth tissue of the two are in contact and grow together The cuts are then tied together and covered with cloth or with a special wax Budding is the process of remov ing a bud from one plant and setting it into the bark of another usually a young seedling SEXUAL REPRODUCTION In sexual reproduction male and female cells called gametes unite to form a single cell called a zygote This zygote then undergoes cell division ultimately giving rise to a new plant body Offspring produced by asexual reproduction are identical to their parent Offspring produced sexually however have two parents and so though they certainly resemble the parents the offspring are not necessarily identical to them Consequently 13
A CLOSER LOOK AT PLANT REPRODUCTION GROWTH AND EcoLOGY sexual reproduction is a process that increases variation among offspring ALTERNATION OF GENERATIONS In plants the process of sexual reproduction takes place in two distinct phases or genera tions In one phase the organism reproduces by means of spores and in the other by means of sex cells This reproductive pattern is called alternation of generations The structure that produces spores is known as the sporophyte Spores are single cells that like the gametes of animals are produced by a type of cell division called meiosis When a spore germinates it pro duces the gametophyte the structure that produces gametes When a male gamete or sperm unites with a female gamete or egg they form the zygote The alternation of generations is perhaps most clearly seen in ferns because the spo rophyte and gametophyte form independent structures The common fern fronds that grow along stream banks are sporophytes They produce spores in structures called sori which are often found on the underside of the plant's leaves When a released spore lands at a place favorable for germination it grows I
METHODs OF PLANT REPRODUCTION A fern gametophyte The gametophytes of sexually reproducing plants are responsible for the production of gametes which each contain one complete set of chromosomes Dr Richard Kessel Dr Gene Shih Visuals Unlimited Getty Images 15
