SWEET- CLOVER SEED. 27 



coats were made readily permeable to water. Gola (6) states that 

 the cause of the impermeability of seeds is the peculiar character of 

 the Malpighian cells, which prevents their infiltration and conse- 

 quent increase in volume, while Bergtheil and Day (2) found that the 

 hardness of the seeds of Indigofera arrecta was due to their possession 

 of a very thin outer covering of a substance resistant to water. 

 Ewart (5, p. 185) believes that in most impermeable seeds the cuticle 

 prohibits the absorption of water, but gives as an exception Adan- 

 sonia digiiata, in which the whole integument seems to be permeable to 

 water with difficulty. The following is quoted from White (42, p. 

 205): 



As a general rule in small and medium-sized seeds the cuticle is well developed 

 and represents the impermeable part of the seed coat, while in the cases of large seeds, 

 such as those of Adansonia gregorii, Mucuna gigantea, Wistaria maideniana, and Guil- 

 andina bonducella, the cuticle is relatively unimportant and inconspicuous. 'In these 

 seeds the extreme resistance which they exhibit appears to be located in the palisade 

 cells. 



In discussing the seed coat of Melilotus alba, Rees (33, p. 404) 

 states that the outer layer consists of palisade cells covered exter- 

 nally by a structureless membrane, which, however, did not appear 

 to be cuticle but hemicellulose, as it stained magenta with chlor- 

 iodid of zinc. The greater part of the walls of the palisade cells also 

 appears to be composed of hemicellulose and the outer ends only 

 were cuticularized. In order to find whether the outer membrane 

 was in itself impermeable to water, this author treated seeds for short 

 intervals in sulphuric acid to dissolve the outside covering without 

 directly affecting the palisade cells. Seeds treated in this manner 

 swelled in water and microscopic examination showed that the ends 

 of the palisade cells were quite intact, but had separated from each 

 other. From this it was concluded that the outer membrane is 

 instrumental in conferring impermeability on the seed, although not 

 directly responsible for it, as is the case with a true cuticle. It is 

 further believed that it probably served as a cement substance by 

 means of which the cuticularized ends of the cells were held together 

 closely, thus forming a barrier through which water could not pene- 

 trate, but that as soon as this barrier was removed the ends of the 

 palisade cells separated and water passed in between them. 



More than 20 years ago machines were devised by Kuntze, Michal- 

 owski (27, p. 86), Huss (15), and later by Hughes (14), to scarify 

 impermeable seeds. Other methods have been recommended and 

 employed to some extent for hastening the germination of seeds. 

 Hiltner (13, p. 44) treated seeds of red clover, white clover, and 

 alfalfa 10, 30, and 60 minutes with concentrated sulphuric acid and 

 found that the best germination resulted from the 60-minute treat- 

 ment. Love and Leighty (21) also treated the seeds of various 



