Wilting is not always caused by water loss; it can also occur as a result of certain
wilt diseases, caused by both fungi and bacteria. Plants grown in saline soils can also
often become wilted even though the soil may have enough moisture, discussed in 1Ca.
All plants need light in order to grow, but the amount of light they need varies according
to the species and the growth stage of the plant. For example groundnuts (peanuts) like
to have plenty of light during germination and early growth, but during flowering and
maturation they can grow well in some shade. In practice this means that groundnuts can
be intercropped with taller plants such as wheat provided that the wheat does not shade
the groundnuts early in their life cycle.
Other plants such as pigeon peas and most of the cereals require full lighting during
their entire life cycle if they are to grow well—these are the so-called sun plants. Their
leaves display a higher light saturation point and maximum rate of photosynthesis.
By contrast shade plants such as the peppers (Capsicum spp.) will grow well in
lightly shaded places such as under trees. In general, their leaves are thinner, have more
surface area and contain more chlorophyll than the leaves of sun plants.
The effect of Temperature
Sunlight is only one factor which influences plant growth. Temperature is another.
Although some crops such as tomatoes and onions prefer full sunlight—the “sun plants”
described above—they also suffer from excessive temperatures. So in very hot regions
tomatoes will actually grow better in lightly shaded places protected from the full heat
of the sun, even though they are normally considered as sun loving plants.
Legumes also prefer to grow in full sunlight, but in very hot sunny places they will
also grow well if they are lightly shaded.
Sometimes even different varieties of the same crop species have different
requirements for light and temperature.
This is a good example of the subtlety of understanding required by people who
grow food. They cannot blindly follow rigid rules and expect consistently good crops,
but should be aware of the different needs of different plants for light, temperature,
water, air, soil etc. and then attempt to regulate these factors as far as practical.
Also known as vegetative propagation (multiplication) or asexual reproduction, this is
the form of reproduction in plants that does not involve a flower, seed or any sexual
process but involves removal of part of the plant. This part is then placed in soil, or
water, where it develops into a new plant, identical to its parent.
This form of reproduction perpetuates plants of uniform appearance, quality etc. for
many generations (although occasionally a mutation occurs to change this, such as the
sudden unexpected appearance of a red tuber in a white variety of potatoes).
There are both pros and cons of vegetative propagation as opposed to propagation
by seed, described below:
40 TONY WINCH
1Eg. Shade Plants / Sun Plants