JODRNAL OF AGRICULTURAL RESEARCH 



DEPARTMENT OF AGRICULTURE 



Vol. VI Washington, D. C, August 14, 1916 No. 20 



AGRICULTURAL VALUE OF IMPERMEABLE SEEDS 



By George T. Harrington, 



Scientific Assistant, Seed Laboratory, Bureau of Plant Industry 



INTRODUCTION 



During the years 1909 to 1916, inclusive, many germination tests of 

 lots of clover and alfalfa seed were made for the purpose of determining 

 the agricultural value of the impermeable seeds. A smaller number of 

 tests of winter vetch, okra, and other seeds were made for the same 

 purpose. 



Impermeable seeds, in the sense in which the term is used in this 

 paper, are seeds whose coats are impermeable to water at temperatures 

 favorable for germination. In the majority of plants which produce 

 impermeable seeds this feature of the seed coat results from the peculiar 

 character of its outer layer of cells, which may, in addition, be covered 

 by a continuous cuticle. , 



Such seeds have been aescribed by numerous investigators, including 

 the present author, under the term "hard seeds." Guppy (9) 1 has, 

 however, introduced a more appropriate term, "impermeable seeds," 

 which will be used in the present paper. The term is relative, as imper- 

 meable seeds are capable of becoming permeable. While in the imper- 

 meable condition they remain very hard and dry, even when surrounded 

 by water. When they become permeable, they absorb water readily, 

 becoming soft and swollen. Naturally no seed can germinate while in 

 the impermeable condition. In speaking of the germination of imper- 

 meable seeds, therefore, one means simply the germination of seeds 

 which were impermeable at some previous time. 



Many species of plants produce both impermeable seeds and seeds 

 whose coats are readily permeable to water at one or more points. 

 According to Guppy (9), these two types of seed can easily be distin- 

 guished by structural differences in certain plants (Entada polystachya and 

 Axyris amaranthoides) , but this is not true of any of the plants considered 

 in this paper. 



Verschaffelt (18) has investigated the relative permeability to both 

 water and other liquids of different areas of the seed coats of a large 



1 Reference is made by number to "Literature cited," p. 796. 



Journal of Agricultural Research, Vol. VI, No. 20 



Dept. of Agriculture, Washington, D. C Aug. 14, 1916 



ey G — 91 



(761) 



