iyjol 



JO MLS— MAPLE SEEDS 147 



maple. Numerous observers have reported cases of seeds dying 

 when subjected to atmospheric conditions for a short period of 

 time. As to just what factors operate with desiccation to cause 

 lowering of seedling vigor and early death we are still entirely 

 ignorant. In the river maple temperature does not appear to 

 determine the critical percentage of water loss. Death occurs at 

 all ordinary temperatures (0-3 5 C.) when the percentage of water 

 in the seeds has reached 30-34 per cent. Whether or not this will 

 hold in general for other seeds of this type will not be known until 

 considerably more species have been studied. In the desiccated 

 seeds we find a noticeable increase in permeability, indicated by 

 a large amount of sugar appearing in the substratum when placed 

 in the germinator. The sugar makes an excellent medium for 

 growth of bacteria and fungi, and in a few days the entire seed is 

 completely decomposed. The fungi appear to be unable to attack 

 potentially vigorous seeds. Whether increased permeability is 

 the cause or the result of death is not known. Desiccation may 

 coagulate or denature the protoplasmic proteins, increasing per- 

 meability and subsequent leaching, allowing an inroad for parasitic 

 organisms. This type of seed stands in marked contrast to that 

 type of seed which retains its viability best when stored in an 

 air-dry condition. Duvel (10) even recommends drying the 

 majority of seeds in a vacuum or over sulphuric acid to insure 

 good preservation. In fact, many seeds can be dried to constant 

 weight without lowering viability or seedling vigor. Kidd (15) 

 states: "In the case of certain rapidly deteriorating seeds (Hevea 

 brasiliensis) the carbon dioxide naturally produced by respiration 

 of the seeds in a closed flask rose to 40 per cent, and the pressure 

 of this was found to be accompanied by a marked prolongation of 

 vitality in the seeds. This prolonged vitality was far in excess of 

 that reached with the present commercial method of packing these 

 short-lived seeds for export." Where there is a rapid oxidation 

 of food material due to high respiration, there is no doubt that 

 narcotizing the embryo would result in greatly reduced metabolic 

 activity. Whether or not high embryo vigor can be maintained in 

 the river maple by narcotizing still remains to be determined. 

 Storage at o° C. over water, however, provides an excellent con- 

 dition for the seeds of river maple. 



