Description
of seeds belonging to the Angiospermae
Parthenocissus quinquefolia (L.) Planchon Virginia creeper (Vitaceae) Sow immediately after the harvest in the autumn, or, preferably, in the spring with seeds stratified for 2 months. Vegetative propagation widespread.
Parthenocissus tricuspidata (L.) Planchon Boston Ivy (Vitaceae) See P.quinquefolia.
Paulownia tomentosa Steud (Bignoniaceae) The seeds of this species have no dormancy but they need light in order to germinate. It is nevertheless possible to acheive rapid germination, even in the dark, if the seeds are vernalized for 2 months before sowing in seed beds in the spring. If the seed is kept in the stratification substrate at +4°c with an adequate level of humidity, its vitality remains virtually unaltered for 18 months. An effective method to combat funghi and bacteria present in the seed integuments is to soak the seeds in a solution with 5% of sodium hypochlorite for 20 minutes, and then rinse prior to sowing or stratification.
(Oleaceae) Sow in the autumn immediately after the harvest. The pulp should be removed from around the seed, which should then be scarified mechanically or chemically (concentrated sulphuric acid for 30 minutes). Vegetative propagation possible.
(Oleaceae) Vegetative propagation possible. See P. angustifolia.  Fruits of Phillyrea latifolia
Phoenix canariensis Chabaud canary palm (Palmae) Sow in warm beds in the spring, at temperatures from +20 to +25°c, and constant humidity but good drainage. Germination speed may be improved by removing the pulp and soaking the seeds in lukewarm water for 24-72 hours prior to sowing.
Pittosporum tobira (Thunb.) Aiton (Pittosporaceae) Sow in autumn/winter in protected seed beds and transplant in the spring, or sow in the spring. Vegetative propagation possible.
(Platanaceae) Seeds are usually sown in the spring with seeds vernalized for 45-60 days. It is advisable to protect against soil fungi and birds.
Platanus occidentalis L. American sycamore (Platanaceae) See Platanus spp.
Platanus orientalis L. oriental plane (Platanaceae) See Platanus spp.
Poinciana gilliesii Boj ex Hook (Leguminosae) See Acacia spp.
(Rosaceae) The seeds of the many species of Prunus often have an endogenous type of dormancy and require a period of post-ripening in a warm, moist, airy atmosphere. Furthermore, the hardness of the endocarp may offer resistance against germination. Pretreatments vary according to provenance and species, and are not always effective. Straight after the mature fruit have been harvested, the pulp must be removed, above all to prevent the growth of moulds, and prevent depredation by birds and rodents. The water content of the seed to be stored should be maintained from 6-15%, usually 9-10% at temperatures from -3 to -1°c. Before stratification or storage, fungicides may be applied. Since high soil temperatures may induce secondary dormancy in pretreated seeds, we advise against late spring sowing.
(Rosaceae) The quality of the seeds may be maintained for 3-4 years, if the seed matter is stored at temperatures of between -5 and -1°c with a water content of 8%. Since the mechanisms which regulate dormancy are not fully understood, suggestions as to pretreatment are at times contradictory. There follows, however, a list of the most common sowing practises:
In each of these cases, it is a good idea to check the seed matter frequently in order to interrupt the treatment before 5-10% of the seeds have put out rootlets. If theroregulated environments are available, it is better to use methods d) and e), which allow the treatment to be lengthened for a few weeks (3-8) at temperatures of -3°c, if it is necessary to postpone sowing. High temperatures in the topsoil (+20°c), even for relatively short periods (7-14 days), induce secondary dormancy. Sowing should therefore be carried out at the end of the winter - early spring, if possible with mulching with straw or peat. Before sowing vernalized seed, most of the bad seeds can be separated first by floating. Recent studies suggest that thermal treatments may be carried out without a substrate, and that non-dormant seeds may also be stored for long periods at -5°c after dehydration to 8%. See Prunus spp.
Prunus cerasifera Ehrh. (Rosaceae) Sow in the autumn with seeds stratified in the warm for 2-4 weeks (begin the treatment straight after the harvest) or stratified in natural conditions from the moment of harvesting. Alternatively, sow in the spring with seeds which have undergone warm stratification for 2 weeks and cold stratification for 11-14. Interrupt the treatment as soon as germination begins. See Prunus spp.
Prunus laurocerasus L. cherry laurel (Rosaceae) Sow in the autumn or in the spring with seeds which have been vernalized for 2 or 3 months. There are many cultivars obtained via vegetative propagation : ‘Caucasica’, ‘Herbergii’, ‘Magnoliifolia’, ‘Mount Vernon’, ‘Otto Luyken’, ‘Rotundifolia’, ‘Schipkaensis’, ‘Variegata’, ‘Zabeliana’ etc. See Prunus spp.
Prunus mahaleb L. St Lucie cherry (Rosaceae) Sow in the spring with seed which has been stratified warm for 2 weeks and cold for 11-14 weeks. See Prunus spp.
Prunus spinosa L. sloe, blackthorn (Rosaceae) Sow in the spring with seed which has been stratified in the warm for 2-4 weeks and in the cold for 4-18 weeks. See Prunus spp.  Seeds of Prunus spinosa
Pterocarya fraxinifolia (Poiret) Spach wing nut (Juglandaceae) Some authors consider this seed recalcitrant, so care should be taken to see that it does not dehydrate. Sow in the autumn or in the spring with seed which has been stratified outdoors for 2-3 months.  Seeds of Pterocarya fraxinifolia
Punica granatum L. pomegranate (Punicaceae) Sow in the autumn or in the spring with seed which has been vernalized for 30-60 days. Seed propagation produces generally diverse stock.
Pyracantha coccinea Roemer firethorn (Rosaceae) Sow immediately after the harvest in autumn-winter, then transplant in the spring; otherwise, sow in the spring with seed which has undergone cold stratification for 3 months. The treatment is probably more effective if a period of aestivation is carried out before vernalization. Whole fruit may be used, or the seeds obtained via the soaking of the fruit.
(Rosaceae) See Malus sylvestris.
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