Papillae of the Viola tricolor attractive to insects.

Parsley.

Passiflora alata. —­ gracilis. measurements. crossed and self-fertilised. seeds. self-fertile.

Passifloraceae.

Pea, common.

Pelargonium zonale. measurements. effects of intercrossing. almost self-sterile.

Pentstemon argutus, perforated corolla.

Petunia violacea. measurements. weight of seed. cross with fresh stock. relative fertility. colour. summary of experiments. superiority of crossed over self-fertilised. early flowering. uniform colour of self-fertilised. seeds. self-sterile.

Phalaris canariensis. measurements. early flowering of crossed.

Phaseolus coccineus. —­ multiflorus. measurement. partially sterile. crossed and self-fertilised. early flowering of crossed. seeds. perforated by humble-bees. —­ vulgaris. self-fertile.

Pisum sativum. measurements. seldom intercross. summary of experiments. self-fertile.

Plants, crossed, greater constitutional vigour.

Pleroma.

Polemoniaceae.

Pollen, relative fertility of flowers crossed from a distinct plant, or with their own. difference of results in Nolana prostrata. crossed and self-fertilised plants, again crossed from a distinct plant and their own pollen. sterile with their own. semi-self-sterile. loss of. number of grains in Dandelion, Paeony, and Wistaria sinensis. number necessary for fertilisation. transported from flower to flower. prepotency. aboriginally the sole attraction to insects. quantity produced by anemophilous plants.

Polyanthus, prepotency over cowslip.

Polygoneae.

Posoqueria fragrans.

Potato.

Poterium sanguisorba.

Potts, heads of Anthornis melanura covered with pollen.

Primrose, Chinese.

Primula elatior. —­ grandiflora. —­ mollis. —­ officinalis. —­ scotica. —­ sinensis. measurements. early flowering of crossed. —­ veris (var. officinalis). measurements. result of experiments. early flowering of crossed. seeds. self-fertility. prepotency of dark red polyanthus.

Primulaceae.

Pringlea.

Proteaceae of Australia.

Prunus avium.
—­ laurocerasus.

Pteris aquilina.

Radish.

Ranunculaceae.

Ranunculus acris.

Raphanus sativus.

Reinke, nectar-secreting glands of Prunus avium.

Reseda lutea. measurements. result of experiments. self-fertile. —­ odorata. measurements. self-fertilised scarcely exceeded by crossed. seeds. want of correspondence between seeds and vigour of offspring. result of experiments. sterile and self-fertile.

Resedaceae.

Rheum rhaponticum.

Rhexia glandulosa.

Rhododendron, spontaneous crossing.

Rhododendron azaloides.

Rhubarb.

Ribes aureum.