parasitism, 752, 761, 762, 763, 

 764; 766, 768, 760, 770, 771, 775, 780, 

 786 ; alternative, 787 ; conduction, 688 ; 

 facultative, 762 ; obligate, 762 ; partial, 



761, 771; reciprocal, 752, 786; water, 



762, 771. 



Parenchyma, conductive, 682 ; sheath, 683. 

 Parthenocarpy, 917. 

 Parthenogenesis, 823 ; artificial, 882. 

 Partial parasites, 761, 771; saprophytes, 



754- 



Passage cells, 683. 



Passiflora; passion vine, nectaries, 858. 

 Pathogenic bacteria, 762. 

 Pea, leaves, 640; root tubercles, 788; 



stipules, 641. 

 Peat bogs, 942. 

 Pedicel, 833, 874. 

 Peduncle, 874, 921. 

 Peg rhizoids, 516. 

 Pelargonium, glandular hairs, 623. 

 Pellionia, cystolith, 626. 

 Pendulous organs, 657, 703. 

 Pentarch bundles, 683. 

 Penthorum, rhizomes, 670. 

 Peony, flower, 826. 

 Peperomia, leaf section, 632. 

 Peppergrass, leaf section, 530; roots, 498; 



rosettes, 582. 



Perennial, 501 ; herbs, 713, 716. 

 Perianth, 825, 826, 827, 833, 871, QO2, 903. 

 Pericambium, 683. 

 Pericarp, 906, 915. 

 Periclinal chimera, 780. 

 Pericycle, 683, 696. 

 Periderm, 705, 706. 

 Peridium, 812. 

 Perigynous flowers, 828, 854. 

 Period, acceleration, 690; maturity, 690; 



retardation, 690. 

 Periodicity, 735, 736, 737, 881, 885, 889, 



890. 

 Peripheral chlorenchyma, 630, 631; water 



tissue, 533, 632, 635. 

 Perisperm, 905, 906. 

 Peristome, 814. 

 Peronospora, haustoria, 763. 

 Persimmon, endosperm, 913. 

 Petal, 825, 826, 853. 

 Petalization ; petalody, 901, 902. 

 Petiole, 507, 521, 540, 541, 542, 579, 640, 



641, 728, 833-. 



Petunia, flower, 859; pollination, 841. 

 Phaeophyll, 522. 

 Phagocytosis, 798. 

 Phaseolus, regeneration, 748; seed section, 



905; twining stem, 651. 

 Phelloderm, 705 

 Phellogen, 553, 661, 705. 



Phenology, 887. 



Philadelphus, flowers, 825. 



Philodendron, roots, 512, 513. 



Phlegethonius, 841. 



Phloem, 530, 630, 682, 683, 684; second- 

 ary, 684; sheath, 683. 



Phloeoterma, 683. 



Phoenix, seedling, 935. 



Phoradendron, 777. 



Phosphorescence, 760. 



Photeolic movements, 579. 



Phototropism, 539, 540, 542, 544, 546, 547. 



Phryma, flowering shoot, 875. 



Phylloclade, 666. 



Phyllode, 590, 640, 937. 



Phyllotaxy, 510, 542, 543, 549, 595, 641, 

 642, 647, 714. 



Physcia, 800. 



Physiographic ecology, 485. 



Physiological ecology, 485 ; species, 765. 



Physocarpus, exfoliation, 709. 



Picea, 648. 



Pigments, 522, 528. 



Pigweed, winged, 922. 



Pilea, stoma, 559. 



Pine, habit, 584; leaf section, 724; second- 

 ary wood, 690. 



Pinguicula, 618. 



Pinna, 754. 



Pinnule, 636. 



Pinus, habit, 584; leaf section, 724} 

 secondary wood, 690. 



Pistil, 825, 826, 851, 853. 



Pistillate flowers, 833, 834, 837, 861. 



Pisum, root tubercle, 788. 



Pit, 679, 680, 68 1 ; bordered, 680, 690; 

 stomatal, 557, 558, 567, 724. 



Pitcher plant, 618. 



Pith, 680, 685, 769. 



Pitted vessel, 681. 



Plagiotropic organs, 748. 



Plane rhizoids, 516; vernation, 937. 



Plank roots, 509. 



Plantago; plantain, flowers, 835. 



Plant associations, 939, 940, 942, 943, 944, 

 945- 



Planting of seeds, 928. 



Plastid, 522 (see also Chloroplast). 



Platanus, bud protection, 640. 



Plate, sieve, 681, 682. 



Plicate vernation, 937. 



Plowrightia, gall, 784. 



Plumule, 905, 906, 931, 935. 



Plurivore, 765. 



Poa, leaf section, 531 ; stoma, 556. 



Pocket, root, 510. 



Pod, 865, 919, 920. 



Poinsettia, nectary, 844. 



Polarity, 749, 750; reversal, 750, 751. 



