1922] EVANS—GERMINATION 215 
These coat effects may be of several kinds, namely, the almost 
complete exclusion of water from the embryo, as in some Legumin- 
osae, the cutting down of oxygen supply below the minimum 
required for germination (9), or the high elasticity or breaking 
strength of the coats as compared with the force of the expanding 
embryo (3, 4). 
CROCKER (3) and Crocker and Davis (4) state that this last 
named coat effect is the chief cause of dormancy in seeds of Amaran- 
thus retroflecus. This dormancy gradually disappears in dry 
storage, as is shown by a continual lowering of the minimum 
temperature for germination. On the other hand, wild oats, 
“rain barley,” and a South American grass, Chloris ciliaia, have a 
low maximum when not after-ripened, which rises as after-ripening 
progresses. Even in seeds of Amaranthus retroflecus which have 
been stored for a long time, incompleteness of after-ripening is 
indicated by the considerable lingering effects of the coats. Fully 
after-ripened seeds have their minimum for germination lowered 
by removal of coat restrictions. In fresh A. retroflexus seeds 
with coats treated, the minimum temperature for germination 
is the same as in dried seeds with coats treated. Vigor of the 
embryo of A. retroflexus, ability to respond in germinative condi- 
tions, and the rate of growth of the naked embryo under any given 
conditions is not affected noticeably by after-ripening. In this 
seed after-ripening seemingly is not a matter of after-ripening of 
the embryo, for embryos of fresh seed are of maximum vigor if 
coat effects are removed. That the breaking strength of these 
coats is lowered by a rise in temperature is shown by the fact that 
ripe seeds gathered from green plants will not germinate at temper- 
atures lower than 40° C., but will germinate slightly at that temper- 
ature. A. retroflexus seeds are slightly inhibited by light at all 
temperatures, according to the unpublishéd experiments of CROCKER 
and Davis. This holds for seeds in which the coats are treated 
as well. Knowledge of these conditions was requisite to han- 
dling the material intelligently in finding the series of coefficients 
relating rate of germination of A. retroflexus to temperature . 
changes. 
