8o 



from them and the sap expressed in large enough quantities that it 

 could be evaporated down to one-fourth to one-eighth of its volume 

 and leave enough for freezing point determinations with a Beckmann 

 thermometer. The evaporating was done in a dry oven where the 

 temperature never was above 50° C. The evaporating was done in 

 broad, shallow dishes and was generally accomplished in one day. 

 There was apparently no fermentation. In all cases sap taken in 

 October or early November would be thick and gummy long before 

 it could be concentrated to one-sixth of its original volume. It was 

 noticed that it was very difficult indeed to filter the sap from the twigs 

 in autumn or very early winter, while sap taken in December or Jan- 

 uary or later, filtered much more easily and could be concentrated 

 to one-sixth to one-eight of its volume. In this case it would stay 

 in solution at temperatures as low as could be secured with salt and 

 ice; that is, temperatures low enough to kill many peach buds, indi- 

 cating that there is certainly a probability that at least a part of the 

 sap solute remains in solution at a temperature low enough to hold 

 water unfrozen to protect the protoplasm. Of course in the earlier 

 season the solidifying of the liquid may be due to colloidal substances 

 in large quantities, and it is entirely possible that the solute had just 

 as low an eutectic point. It was not possible to determine the eutectic 

 point by keeping temperature records since no apparatus was availa- 

 ble other than the Beckmann thermometer which could not be used 

 without changing the setting several times, for such low temperature. 

 It would seem highly probable that, except in the case of cam- 

 bium, the additional hardiness acquired by the different tissues of 

 the tree as they pass into winter, is a change in the protoplasm such 

 that it can withstand the great loss of water rather than a change in 

 the percentage of moisture or in sap density. It is also possible 

 that changes in the sap solute that lower its eutectic point may occur 

 and that these may increase the resistance to cold by holding water 

 unfrozen to protect the protoplasm from too complete desiccation at 

 lower temperatures. 



Rate of Growth and Hardiness. At the time of most rapid 

 growth of deciduous plants in early summer they are generally most 

 tender. Whether this is because they are furthest from the con- 

 dition of maturity they acquire in autumn and early winter, or be- 

 cause of the very low sap density at this time, it is not easy to say. 

 In some cases the young tissue is most hardy. Thus Goeppert 

 found young leaves more haifdy than older ones. Apelt 1 found the 



•Oohn. Beitrage z. Biol. d. Pfl. Vol. 9, p. 215. (Blbl. No. 3). 



