6 HORTICULTURAL SOCIETY OF XEW YORK. 



that as the temperature decreases, growth slows down until an 

 infra-optimum is reached at which growth ceases as it did at a 

 certain point above; this is the temperature of fatal cold at 

 which living matter is totally disorganized. 



Our efforts at acclimatization and our work in securing the 

 feature of hardiness in plants, with respect to temperature, con- 

 sist in operations by which the position of the cardinal points of 

 the plant with which we may be working may be altered on the 

 scale of the thermometer. These cardinal points undergo wide 

 changes in a state of nature, and it is by taking the inherited 

 capacity for adaptation of any plant wuth regard to this particu- 

 lar into account that we may hope to make our greatest prog- 

 ress. First of all it is obvious that these five critical points in 

 the life of any plant change with the development of the indi- 

 vidual, and that the optimum slides up or down the scale, or all 

 open out more widely. Take any plant, such as the radish, 

 wheat, squash or sunflower, and it has been found that seed or 

 grains air-dry, and in resting condition, may endure the lowest 

 cold that can be produced, that of liquid hydrogen at about 454° 

 F. below the freezing point of water, which proves that the fatal 

 cold in such cases is extremely low, and to have only a theoreti- 

 cal existence. The same seeds in a resting and dried condition 

 may be subjected to the heat of boiling water at 212° F., so that 

 the points of fatal heat and cold lie far apart in this stage of the 

 existence of the plant. Now give them a supply of moisture 

 and start germination, and a radical change in the position and 

 relation of the critical points ensues. A cold fatal to the active 

 seedling wull be found near the freezing point of water, and but 

 slightly below the infra-optimum, the optimum will be found to 

 lie between 80° and 98° F., the supra^optimurn and cessation 

 of growth will be found between 100° and 120° F. for most 

 plants, although many species, especially those native to the 

 desert, range higher, while a fatal heat comes within a few de- 

 grees above the supra-optimum. 



As the plant nears maturity, the tissues harden, the proto- 

 plasm becomes more highly granulose and denser, and has an 

 altered chemical composition, by which it again becomes less sus- 

 ceptible to alterations, and again the cardinal points take posi- 



