Embryo Dormancy of Pinus jeffreyi Murr. Seed as Affected by Temperature, Water Uptake, Stratification, and Seed Coat.

Almost three hundred years ago the English siivi-. -culturist, John Evlyn (7), recognized the general problem of forest tree seed dormancy. He did not discuss dormancy as such, but he did report that fall or early winter sowing of acorns, beech-nuts, haws and holly berries was a better practice than spring sowing. He went on to state that "... seeds may be prepared for the Vernal by being barrell'd or potted up in moist sand or earth stratum during the winter at the expiration whereof you will find them sprouted and being committed to the earth as apt to take as if they had been sown with the most early ... and will not be much concern'd with the increasing heat of the season, as such as being crude, and unfermented are newly sown in the beginning of the Spring. . . ." Thus, here is perhaps the first published recommendation for artificial stratification of dormant tree seed. It is obvious he did not know why it was effective?as a matter of fact, we do not know why today, even though we have recognized some of the associated biochemical changes (6,8, 11, 12, 14). Since the turn of the century numerous studies on seed dormancy have been reported; see reviews by Miller (11), Baldwin (1), Crocker (4), and Crocker and Barton (5). Specific reference to pine seed indicates that the dormancy mechanism of that seed is not entirely clear. For example to overcome dormancy, at least five different pregermination treatments have been recommended. They are: soaking the seeds in sulfuric acid (17); soaking the seeds in water at room temperature (9) ; soaking the seeds in water at low temperature (15, 16); cold storage in wet sand or peat moss (2, 3, 13, 23) and removal of the seed coat and papery membrane (19). The most widely used method of increasing seed germination is the low-temperature moist storage treatment generally referred to as stratification. During this particular type of pretreatment chemical changes apparently take place in the seed, after which the seed germinates. For example, Eckerson (6) found during stratification of Crataegus mollis seeds that the fats decreased while there was a progressive increase in sugars, acidity, catalase activity, peroxidase activity, and water-holding capacity. Similar results are reported by Pack (14) for seeds of Juniperus virginiana, J, communia and J. prostrata. He found that fats and proteins decreased while sugars, amino acids, catalase activity, and respiration all increased during stratification. On the other hand Koblet (10) found little change in the character of the food reserve in Pinus strobus seeds during stratification. Only a slight increase in reducing sugars, amino acids, and soluble nitrogen was noted. From this he concluded that the low temperature treatment facilitated a faster mobilization of the reserves during germination and ". . . that low temperatures could effectively stimulate the plasma or upset its equilibrium thereby giving an impulse to growth." The major change Mirov (12) found* in stratified Pinus lambertiana seeds was an increased saturation of the fats. His data also suggested a build-up of auxin in the endosperm during stratification ? a change which Haddock (8) subsequently was unable to detect.