478 A TEXTBOOK OF 
male gametophyte and fertilization 
ot, 425; megasporangium and female 
prothallus of, 422-423; microspo- 
rangium of, 4238 ; pollination of, 423— 
424; resin duct of, 124*; seed of, 
425-427; vegetative structure of, 
421-422 
Pineapple, 83, 204, 277 
Pinne, 73 
Pinnate leaf, 72*, 73 
Pinus flexilis, 445* 
Pinus insularis, 420*, 423* 424*, 426* 
Pistia stratiotes, 11*, 32*, 459* 
Pistil, 6, 205 ; in sexual reproduction, 5 
Pisum sativum, 77-78, 79, 81*, 236- 
242, 250 
Pitcher plants, 83-86 
Pith, of Coniferales, 420-421; of di- 
cotyledonous stele, 120 
Pith rays in dicotyledonous stem, 126, 
144, 148-149 
Pithecolobium dulce, pods of, 276* 
Pitted vessels, 122 
Plants, aquatic, 80; breeding of, 248- 
256 ; classification of, 211-214; defi- 
nition of, 34; dicecious, 206-207 ; 
divisions of, 804; geography of, 1; 
moncecious, 206-207 ; respiration of, 8 
Plasma membrane, 41-42 
Plasmolysis, 41-42 
Plastids, 24 
Platycerium biforme (staghorn fern), 90* 
Pleodorina illinoisensis, 321 
Plumule, 279 
Pocket leaves, 89 
Pod, 276*, 277-278 
Poinsettia (Huphorbia pulcherrima), 88, 
163, 456; flowers of, 87*, 217* ; latex 
tube of, 126* 
Poison in stinging hairs, 76 
Polar nuclei, 222, 431 
Poles, 224-226 
Pollarding, 107 
Pollen, 218-219 ; of angiosperms, 431— 
432 ; of Cycadales, 409-410 ; of pine, 
423-424 ; in sexual reproduction, 5 ; 
of Spermatophyta, 403, 404; trans- 
fer of, 5. See Microspores 
Pollen grains, 206, 208*, 229 
Pollen mother cell, 229 
Pollen sacs, 206,404; of angiosperms, 430 
Pollen tubes, 6, 221, 405, 415* ; of pine, 
425, 427% 
Pollination, 5-6, 95, 206, 207, 209, 216*, 
218, 221; in leafless forest, 442 ; of 
pine, 423-424 
GENERAL BOTANY 
Polypodium sinatum, branch of, 173* 
Polysaccharide, 290 
Polysiphonia violacea, 342* 
Polystele, 387 
Poppy, capsule of, 285* 
Pore fungus, 360*, 363 
Porphyra, 342* 
Portulaca oleracea, 221* 
Positive geotropism, 108 
Positive phototropism, 109 
Potassium, 175 
Potassium hydroxide, absorption of 
earbon dioxide by, 51-52 
Potato, starch grains of, 45*, 290*; 
sweet, 203 ; tuber of, 175*, 288 
Potential energy, 48 
Primrose, 241 
Prop roots, 199-201 
Prophase, 224, 226; in heterotypic mi- 
tosis, 229-231 
Prosopis velutina, 66* 
Protection, 78, 174; of leaves, 90; of 
stem, 165 
Proteins, 18, 124, 140, 288*, 289*, 291— 
293, 294*, 295 J, 
Prothallial cell, of Cycadales, 409 ; of 
pine, 425 
Prothallus, female, and megasporan- 
gium of Cycadales, 409 ; female, of 
orchid, 429*; of ferns, 388, 389, 392, 
393*; male, and fertilization of 
Cycadales, 409-410; of pine, 422- 
423, 425*, 426*; of pteridophytes, 
383, 395; of Selaginella, 400-401 ; 
of Spermatophyta, 405. See Micro- 
spores 
Protobasidii, eciospores of, 3857-358 ; 
life history of, 8357-359, 362-363 
Protococcus, 322* 
Protoplasm, 15-25 ; absorption by, 20, 
21, 39; colloidal state of, 18-19; con- 
necting strands of, 24, 25 
Protostele, 385-388, 398* 
Protoxylem of dicotyledonous stele, 
121 
Pruning, 114, 156, 157 
Psidium guajava, branches of, 96*, 100* 
Pteridophyta, 804, 883-402; and An- 
thocerotales, 381; classes of, 385; 
and conifers, 427; and Cycadales, 
409, 415; Hquisetineae, 398, 399; 
fertilization of, 3893*; Filicineae, 
385-398 ; interrelationship of, 402 ; 
Lycopodineae, 399-402; and Musci, 
381; and pine, 425; and Sperma- 
tophyta, 403, 404 
