SEED GERMINATION 237 



ever, changes in the protein fraction of seeds take |)lace. A decrease 

 in true protein content and an increase in low moIeciUar-weight com- 

 pounds such as amines, amides, and amino acids have been shown to 

 occur. This has been interpreted as indicating that the longevity of 

 seeds depends on the retention of the original structure of their 

 proteins. As soon as too many of the original proteins have degen- 

 erated, it is no longer possible for the seed to germinate since it cannot 

 form the new nitrogen compounds, particularly proteins, essential for 

 the development of the embryo. This theory is unproved but at least 

 has some grounds for credibility. If protein degeneration results in the 

 production of compounds from which the proteins of enzymes can no 

 longer be formed, the seed will not germinate. 



Inhibitors 



Some freshly harvested seeds contain compoimds that check or even 

 inhibit seed germination. During dry storage of the seed, these in- 

 hibitors either volatilize or decompose, so that, when the seed is 

 exposed to the proper environment, germination will occur. Inhibitors 

 occur in the coats of fresh lettuce seeds, in the woody materials of 

 the seed balls of beets, and in the fleshy fruits of tomato and cucum- 

 ber. The fact that seeds will not germinate while in fruit, but retain 

 their ability to germinate after the fruit covering has been removed, 

 is explained by the presence of inhibitors. These chemical inhibitors 

 include such substances as ammonia, hydrocyanic acid, coumarin, 

 parascorbic acid, essential oils, and some alkaloids. 



Special Seed Treatments 



Treatment of seeds in order to control certain plant diseases, par- 

 ticularly diseases caused by fungi, has been practiced for many years. 

 Copper sulfate was used as a seed fungicide as early as 1761. Since 

 that time many other copper compounds, including the carbonate, 

 oxide, chloride, oxychloride, and arsenate, have been used with varying 

 degrees of success. Copper compounds have been particularly effective 

 in controlling such diseases as binit and stinking smut of wheat. 



Many inorganic and organic compounds of mercury have been 

 used to control diseases of seeds and tubers. Mercinic chloride, for 

 example, has been employed extensively for the treatment of seed 

 potatoes to prevent scab and for the treatment of wheat to control the 

 Fusarium organism. Organic mercinials have been used to treat corn, 

 peas, wheat, oats, and other seeds. Many commercial preparations, 

 such as Ceresan, New Improved Ceresan, Semesan, Special Semesan, 

 Upsulum, and Agrox, are available in this country and are valuable 



