th and presses others into the ground so that the harrow
following can get a grip on them. It is a harrow that can be made on
any farm. This planker is an excellent tool to smooth the surface, for
broadcasting small seeds and for planting truck crops.

ROLLING

The objects of rolling are:

To compress the surface soil so that the harrow will do its work more
efficiently, also to break clods or lumps that may have resisted the
action of the harrow.

To smooth the surface of the soil for an even distribution of small
seeds, and to firm the soil around such seeds after they are planted
so that they will keep moist and sprout readily.

To give compactness to soils that are light and loose and thus enable
them to hold moisture and plant food better.

To press into the ground the roots of plants partly dislodged by the
frost.

To remove the conditions favorable to the development of many kinds of
insects.

To sink surface stones so that they will not interfere with harvesting
the crop.

Light porous soils may be rolled at any time, but clay soils can be
rolled to advantage only when they are stiff and cloddy.

Spring-sown grain is often rolled as soon as sown. This is all right
in ordinary spring weather, but if showers are frequent and the soil
is quite moist the rolling should be omitted till after the grain is
up. The same practice will apply to autumn-sown grain also. If the
soil is dry the rolling helps it to pump water up to the seeds. But if
it is moist and showers are frequent the combined action of the
roller and the rain is to make so thick a crust that many of the seeds
will not be able to force their way through it or will be smothered by
poor ventilation. After the grain is up the rolling may be done to
advantage, as it then makes a firm soil about the roots of the plants,
a condition of benefit to grain crops.

The most simple form of roller is a solid or hollow cylinder of wood
fastened into a frame by which it is drawn. Some rollers have spikes
or blunt attachments fastened to their surfaces for breaking clods. A
roller that is quite popular consists of a cylinder of pressed steel.

CHAPTER XIII

LEAVES

FACTS ABOUT LEAVES

We found in an earlier lesson that all of our farm plants have roots,
stems, leaves, flowers, fruit and seeds. We studied the root first as
being the most important part of the plant to the farmer. The seed was
the next part studied, for that was considered th