io6 
WM. CROCKER 
all swell at once, but a few at a time, a considerable percent remaining 
hard and viable even after a decade. Hard seeds become permeable 
very slowly under dry storage, more rapidly in germinators under 
laboratory conditions, and apparently still more rapidly under widely 
fluctuating natural conditions. The means by which this resistance 
to water absorption is secured has been mainly studied in the legumes. 
Here a controversy has arisen as to whether it is due to the cuticle or 
to the " light zone " of modified cellulose of the palisade layer. Perhaps 
there is more evidence in favor of the former for small and medium 
sized seeds, and for the light zone or deeper layers of the palisade cells 
in larger seeds. Either will explain the rather general efficiency of 
surface abrasion or carbonization as means of forcing.^* Ver- 
schaffelt^^ has lately given this controversy an interesting turn. He 
finds that seeds of legumes in general have open micropyles that give 
free access to the water absorbing tissues below and that in addition 
in the subfamilies Caesalpinioideae and Mimosoideae rifts or lacunae 
communicating with water absorbing tissues below are present over 
much of the seed surface. Water fails to enter because it will not wet 
the walls of these openings. It will enter, however, if the seed is first 
soaked for an hour in ethyl alcohol and then placed in water. The 
alcohol readily enters the openings and furnishes a path for the inward 
diffusion of water. The efficiency of alcohol as a forcing agent varies 
much with different legumes, showing slight or no effect in many. 
It is likely Verschaffelt's explanation applies to a portion only of the 
legumes and perhaps not at all to other hard seeds. Moreover Ewart 
finds that in some hard seeds all layers of the integument are highly 
impervious to water and Guppy claims this is prevalent among hard- 
coated forms with large seeds. There is need here of much more 
investigation, especially of non-leguminous seeds. 
For cultivated legumes Hiltner^^ claims that crops ripening in dry 
climates or in dry periods show a larger percent of hard seeds. On the 
other hand Harrington^^ finds that alfalfas and clovers, generally, 
grown on a variety of soils and ripening under most diverse climatic 
conditions, have about 90 percent of hard seeds if hulled by hand, but 
generally less than 20 percent if hulled by machine. The huUer thus 
acts as a rather effective abrasive agent and the study of the machine 
15 Nobbe. See 17. 
1^ Verschaffelt. Rec. Trav. Bot., Neerland. 9: 401. 1912. 
" Hiltner. Land. Forst. Wirtsch. Kais. Gesundh. 3: i. 1902. 
1^ Harrington. U. S. Dept. Agr. Farmers' Bull. 676. 
