SUBJECT INDEX 



689 



Nitrogen — Continued 



role in growth, 450-453, 554> 556, 



558 

 Nitrogen cycle, 457 

 Nitrogen fixation, 454-455 

 Node, 562 

 Non-electrolytes, 1 1 

 Normal solutions, 14 

 Nucleic acids, 72, 421, 445 

 Nucleoproteins, 72, 421, 444-445, 446 

 Nucleus, 78 



Nutation, 653, 654, 662, 665-667 

 Nutrient solutions, 427 



Oat coleoptile, relation of auxins to 



growth of, 572-576 

 Oils, see fats 



Optical activity of sugars, 369-371 

 Optical properties of leaves, 348, 349 

 Organic acids, oxidation of, 519 

 Organic matter in the soil, 248-249 

 Osmosis, 93-94 



mechanism of, 96-99, 103 

 vapor pressure theory of, 98-99 

 Osmotic movement of water from 



cell to cell, 149-150 

 Osmotic pressure, 94, 97, 99, lOO 

 analogies with gas pressure, 99-102 

 at incipient plasmolysis, 136, 138, 



146-147 

 effect of hydration of solutes on, 



102-103 



effect on imbibition, II0-II2 



measurement of, 103-104 



relation to freezing point depres- 

 sion, 103-104 



relation to solution concentration, 



99 

 Osmotic pressures of guard cells, 185- 



186 

 Osmotic pressures of plant cells, 

 diurnal variations in, 142-143, 185- 



186 

 factors influencing, 139-142, 147, 



416 

 magnitude, 1 38-1 40, 296-297, 501- 



502 



Osmotic pressures of plant cells — 

 Continued 

 methods of determining, 136-138 

 seasonal variations in, 143-144 

 Osmotic pressures of sols, 43 

 Osmotic pressures of solutions, 99- 



103 

 Osmotic quantities of plant cells, 144- 



149 

 daily variation in, 293-294 

 relation to movement of water, 

 149-150 



Oxalic acid, 79, 519 



Oxidases, 533-534, 545 



Oxidation of foods, 409, 448-449, 

 509-510, 517-519, 520, 537-538, 

 540, 555, 556, 558 



Oxidative anabolism, 547 



Oxido-reductases, 534-535 



Oxygenases, 533-534 



Oxygen, effect of, 



on absorption of water, 282-283 



on anthocyanin svnthesis, 384-385 



on germination, 630-631 



on growth, 609 



on photosynthesis, 359 



on protoplasmic streaming, 75 



on respiration, 523 



Papain, 471, 477 



Paralyzers, enzymatic, 476 



Partial pressure, 9, 87, 88 



Passage cells, 275 



Passive absorption, 278 



Pectase, 470 



Pectic compounds, 68, 379-38o, 554, 



556, 650 

 Pectinase, 470 

 Peptidases, 472 

 Peptones, 438, 443, 447 

 Pentosans, 375 

 Pentoses, 371-372 

 Peptide linkage, 443 

 Pericycle, 219, 270, 271, 272, 273, 



275, 482, 564 

 Periderm, 650 

 Perimeter law, 180 



