( Originally Published 1920 )
Diseased Seed. Numerous failures in germination may be directly attributed to diseased seed. These may carry infection internally in the form of mycelia in the invaded tissue. Seed may also carry infection material externally in the form of spores or sclerotia adhering to the seed coat.
Age of Seed. In determining the cause of poor germination, the age of the seed is to be considered, for after a certain age limit deterioration sets in. Each kind of seed has its own age limit, which is generally determined by the character of the seed itself, i.e., whether oily or starchy, or lacking in both. Thus the vitality of the minute seed of tobacco is perhaps eight times as great as that of the large oily seed of the castor bean. With many species of seed there are apparently no external symptoms to indicate loss of vitality due to age.
Cultural Conditions. The viability of seed is also largely determined by the conditions under which the previous crop grew. The more vigorous the mother plant the more vitality will there be imparted to its offspring. The vigor of the previous crop depends on favorable climatic conditions, care in cultivation, and in fertilization. Old seed produced in a favorable season may be preferred to fresh seed of an inferior quality produced in a bad season.
Weight and Color of Seed. As a rule, light weight seed is inferior to heavy seed of the same variety. The weight of the seed is influenced by culture, and by imperfect fertilization which results in minute and weak embryos. The comparative weight of seed may be readily determined by the water method. Place the seed in a tumbler filled with water. After shaking and letting it stand for a few minutes, the heavier seed sink and the lighter float. Using this method, Stone has shown that the heavier sinking seed give a higher percentage of germination than the lighter.
The color of the seed does not seem to have any influence on the germination. Darker colored seed is usually preferred to the lighter of the same variety. Color, however, largely depends on the degree of ripeness.
Storage Conditions. The vitality of seed is greatly influenced by storage conditions. The longest lived seed may be ruined by improper storage. The ideal conditions of storage, however, are not always those which favor germination. Seed should be cured or dried before storing. The drier it is the less likely it is to spoil and the higher will be the temperature that it can stand. When large quantities of seed are to be handled by the trucker, it is advisable to build a seed house. The seeds are best kept in strong paper or cloth bags, placed in tin or galvanized iron cans.
Seed Testing. In buying seed we must never take it for granted that the germination will be perfect. To make sure, a sample of the seed should be tested for germination. The simplest method, perhaps, is to sow a definite number of seed in a shallow pan filled with moist sand, and kept covered in a warm, dark place. However, the fact that a seed sprouts does not always imply that it will develop into a normal plant. Hence, allowance should be made for this probability when making a test at home or in the seed laboratory.
Effect of Fertilizer on Seed. With the hope of hastening germination, greenhouse men often apply various fertilizers to the seed bed. This practice cannot be too strongly discouraged, especially when muriate of potash and nitrate of soda are used. These two fertilizers when used in strengths of one per cent. or more, inhibit the germination of the seed, whether applied directly or mixed with the soil. Phosphoric acid or lime, when not used in excess, seems to have no injurious action on seed germination. However, on no account should commercial fertilizers be brought into direct contact with the seed. This is well brought out in Table 16 by Hicks.
Seed Treatment. Since seed is often a carrier of disease it is essential that it be treated before planting. Treating the seed for about ten minutes with sulphuric acid will hasten germination and destroy adhering spores of disease-producing organisms. However, more information is needed before this method can be universally adopted by the green-house grower. In practice, the safest method would be to soak all seed, before planting, in a solution of one part of formaldehyde in 320 parts of water, i.e., one pint of formaldehyde in 22 gallons of water. The soaking is carried on for 10 or 20 minutes, depending on the size of the seed and permeability of the seed coat.