50 MISSOURI AGR. EXP. STA. RESEARCH BULLETIN NO. 17 



HISTORICAL 



Existence of a Rest Period in Seeds. The fact of a rest period 

 or resting phase in seeds has been recognized by practically ever> 

 author of textbooks on plant physiology. Pfeffer 1 says : "Certain 

 seeds are capable of immediate germination, whereas others must 

 first rest for a few weeks, months or even years, even when they 

 are not dry, but are kept under conditions that are favorable for 

 germination." 



Jost 2 says, in explanation of the foregoing paragraph: "It is 

 now definitely known that these variations [in germination] depend 

 on varying degrees of permeability of the testa for water, but we 

 know nothing further as to why seeds which have imbibed water are 

 prevented from germinating. At most we may draw analogous con- 

 clusions from the behavior of resting buds. . . . Undoubtedly 

 internal factors play the chief part in determining the initiation and 

 cessation of the resting period in seeds . . /' 



Rest period experiments with seeds were carried on at the Mis- 

 souri Agricultural Experiment Station in 1907-8. 3 In all, 93 species 

 wer studied. These included annuals, biennials, and both herbaceous 

 and woody perennials. It was found that 50 per cent or more of 

 the species tested had a pronounced rest period. 



Mechanical Stimulation of Seeds. In addition to the effects of 

 the rest period which may prevent the germination of seeds, some 

 have a very hard seed coat after becoming dry, and it is almost 

 impossible for the embryo to force its way out. Also such seeds 

 are almost impervious to water. Such seeds are sometimes treated 

 by cracking them open or filing or boring openings thru the testa. 

 Other methods, such as pricking with a needle, or burning with a hot 

 wire, have been devised, and in many cases satisfactory results secured 

 from their use. Leguminous plants are perhaps more conspicuous 

 than any other group in possessing what are generally known as "hard" 

 seeds. These are seeds which do not germinate readily and, because 

 of this fact, breeding work with such plants, especially red clover, 

 has often been seriously hindered. For rendering the seed coat 

 permeable to water, Williams 4 devised the method of shaking the 



1. Pfeffer, Plant Physiology, Vol. II, pp. 207 and 208. 



2. Jost, Plant Physiology, pp. 341-42. 



3. Howard, W. L., Rest Period Studies with Bulbs and Herbaceous Peren- 

 nial Plants. Mo. Agr. Exp. Sta. Research Bui., No. 15. 



4. Williams, N. Y. (Cornell) Agr. Exp. Sta. Bui. 312, p. 296. 



