Page 76 - Introduction to Agriculture by: Aqleem Abbas

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