LIFE SPAN OF SEEDS 63 



the intensity of the treatment: (a) on the mitotic divisions of the embryos; 

 (6) on the resulting seedHngs. The following are some of the chromosomal 

 and mitotic modifications brought about by these treatments: fragmenta- 

 tion of chromosomes with fragments attaching to other chromosomes oi- 

 remaining unattached and not entering into the constitution of daughter 

 nuclei; change in the number of chromosomes in the daughter nuclei, 

 sometimes resulting in polyploidy; giant nuclei; two nuclei in one cell; 

 globules of chromatin in the cytoplasm; and ring chromosomes. The aged, 

 heated, and irradiated seeds showed the following changes in the resulting 

 seedlings: polyploid plants or parts of plants; new forms of plants, some 

 of them larger and more vigorous than the parents; slower germination; 

 slower growth after germination; death of many seedlings in early stages; 

 greatly increased number of chlorotic seedlings and sterile plants; as well 

 as many other morphological abnormalities. In these treatments, as the 

 nuclear or chromosome abnormalities increase, the morphological abnor- 

 malities also increase. 



Aside from the delicate mechanism of nuclear division we should not 

 forget that some of the most complex organic compounds enter into the 

 make-up of the cell nuclei. These may decompose in storage and in turn 

 upset the nuclear mechanism. Also it is possible that toxic or inhibiting 

 substances accumulated in seeds during storage may upset the nuclear 

 mechanism. The remarkable fact is not that the delicate nuclear mecha- 

 nism or the complex compounds of the nuclei degenerate with time, but that 

 for many seeds under good storage conditions they stay intact for centuries. 



Sure it is that in nature some plants are produced from old seeds, seeds 

 that have lain in the ground for 10, 50, or in some cases, 100 years or 

 more. Since aging seeds produce more and more mutations as they age, 

 we have here one of the means by which nature produces new forms of 

 plants, or carries forward evolution. 



This conception of the degeneration of seeds in storage has the virtue 

 of concrete evidence in its favor; it localizes the significant changes in the 

 nucleus and ties the change up with one of the most delicate cell mech- 

 anisms, mitotic division. If this explanation of seed degeneration is cor- 

 rect, then the best storage conditions for seeds are those that best preserve 

 complex organic compounds of the nuclei and the mitotic mechanism of 

 the embryo cells. 



Literature Cited 



1. AUers, "40-jahrige Keimfahigkeit der gelben Lupine," Forstl. Wochenschr. "Silva," 



1922 : 319. 



2. Avery, A. G., and A. F. Blakeslee, "Mutation rate in Datura seed which had been 



buried 39 years," Genetics 28 : 69-70 (1943). 



3. Barton, Lela V., "Effect of storage on the vitahty of Delphinium seeds," C. B. T. I., 



4 : 141-153 (1932). 



4. , "Storage of some coniferous seeds," C. B. T. I., 7 : 379-404 (1935). 



