A Closer Look at Plant Reproduction, Growth, and Ecology
CHAPTER 1 METHODS OF PLANT REPRODUCTION lants continue to live on Earth by producing new plants This process called reproduction may be sexual or asexual Sexual reproduction involves the union of two different sex cells while asex ual reproduction occurs without a union of sex cells ASEXUAL REPRODUCTION There are various types of asexual reproduc tion Mosses and liverworts for example often contain plant fragments called gemmae in cuplike structures on their leaves or stems Gemmae break loose and can germinate or sprout to establish a new plant which is genetically identical to its parent Most vascular plants that is plants with specialized tissues for carrying water and food can reDroduce by a form of asexual reproduction known as vegetative repro duction For example under the proper conditions pieces of leaf or stem broken from a plant may produce roots and estab lish a new individual Plants that produce
METHODS OF PLANT REPRODUCTION Some plants such as strawberries reproduce by growing offshoot plant stems called runners Shutterstock com runners and stolons often reproduce vegeta tively Runners are stems that run along the ground and stolons are stems that grow erect and then curve over touching the ground at the tip The strawberry produces runners that may establish a new plant The runners can then be broken without disturbing the parent or the new plant II
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
