KINDS OF FREEZING AND FREEZING RESPONSES 509 Tender Plants with Little or No Freezing Tolerance . ... . ... 5 10 Plants with Limited Hardiness ....... ........ .. . .. . ........ . . . . .... ..... ... ... ... 510 Woody Plants which Deep Supercool ... . . . . . . . . ..... . . . . . . . . . . ......... . . . . . . . . . . . . . .. . . . . . . . . ... . . . . . . . . . 511 Woody Plants which Do Not Deep Supercool .. " " .. " " .... " .. ".. 514 METHODS FOR STUDYING FREEZING IN PLANTS 515 Nuclear Magnetic Resonance " .. " SIS Calorimetry . . . . . ... .. . ...... . ... ..... . . ....... " 518 FACTORS AFFECTING THE FREEZING PROCESS ........ , 520 Freezing Point Depression ... .. . ...... . . . . ... . ... .... .... .. 520 Supercooling and Ice Nucleation .... ......... ....... , 520 Ice Propagation and Growth ... . .. .... . . . ... . . ... 522 Freezing and Thawing Rates . ... . , 522 Tissue Hydration . . . . . . . . ........ . . . . . . . . . . . . . . . ....... ....... . . . 523 Cell Walls and Membranes as Freezing Barriers .... .. , 523