Page 76 - Introduction to Agriculture by: Aqleem Abbas
P. 76

Introduction to Agriculture         Notes prepared by: Aqleem Abbas


               decline of nitrogen in the soil. (Some of the losses on agricultural lands are replaced only by
               applying energy-expensive nitrogenous fertilizers manufactured by artificial fixation.) On the
               other hand, the leaching of nitrogen from overfertilized croplands, cutover forestland, and animal
               wastes and sewage has added too much nitrogen to aquatic ecosystems, resulting in reduced
               water quality and the stimulation of excessive algal growth. In addition, nitrogen dioxide poured
               into the atmosphere from automobile exhausts and power plants breaks down to form ozone and
               reacts with other atmospheric pollutants to form photochemical smog.

                                                  TYPES OF FLOWERS


               Complete flower

               Those in which floral part are present e.g. tobacco, brassica, cotton


               Incomplete flower

               Those in which at least one floral part is missing e.g. wheat,rice


               Permanent flower

               In which both male and female parts are present e.g. wheat, rice, flower


               Imperfect flower

               Such a flower which has either male part or female part e.g. maize, date palm.


               Hermaphrodite or perfect flower

               Presence of male and female part on same flower is called perfect flower.


                                                       VARIATIONS

               Variations in a population is the basis for selection. Such variations can be hereditary or
               eniornmental. Without hereditary variations any adverse change in the environment may finish a
               pecies in its natural habitat. Hereditary variations are important for breeding of plants they
               results in permanent hereditable changes in the genotype. Such variation can occur in plants due
               to many factors.

                                                 Chromosomal aberration


               That donot involved changes in number of chromosomes but results from changes in number and
               sequences of gene of chromosomes.

                                                         Mutations
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