iQ2o] JONES— MAPLE SEEDS 131 



must be taken that water does not come into contact with the outer 

 walls of the fruit or integuments, as ice formed on the latter appears 

 to inoculate the subcooled tissue below, and freezing to death results. 



Respiration 



Respiration was determined on newly collected seeds, on seeds 

 desiccated at 25 C, and on germinating seeds. Determinations 

 were made on the desiccating seeds every second day until viability 

 was lost, and for several weeks thereafter. All respiration experi- 

 ments were conducted at 25° C, as this temperature was thought 

 to correspond very closely with the average temperature to which 

 the seeds would be subjected under natural conditions. The 

 method of determining the carbon dioxide given off was that 

 described by Grafe (12), with slight modifications. In general 

 the method consists in pulling carbon dioxide free air over the 

 respiring material through a column of barium hydroxide. The 

 barium hydroxide solution is held by a Reiset tube. The air is 

 drawn through slowly and uniformly. This is accomplished best 

 by the air replacing water which is slowly siphoned out of a large 

 demijohn by means of a capillary tube. At the end of a determina- 

 tion the barium carbonate was allowed to settle and an aliquot 

 part (25 cc.) of the 100 cc. of barium hydroxide was pipetted off 

 and titrated with N/20 oxalic acid. Phenolphthalein was the 

 indicator used. 



If the intensity of respiration may be used as a criterion of 

 metabolic activity, then the seeds of the river maple at time of 

 fall are in high state of metabolism. . In the desiccating seeds there 

 is a fall the first few days in respiratory activity, and then a gradual 

 rise until a maximum is reached. This maximum is retained for 

 several days, then there is a gradual decline, until only a trace of 

 carbon dioxide is given off. This secondary rise in respiratory 

 intensity may accompany increased starch hydrolysis. It will be 

 seen later that accompanying desiccation there is a great increase 

 in sucrose, due to starch hydrolysis. The later fall in respiratory 

 activity is probably caused by a deficiency of water. The greatest 

 respiratory activity was obtained on the desiccating seeds with a 

 water content of approximately 44 per cent. There is no marked 



