1906] CROCKER—DELAYED GERMINATION 267 
cave on the inner. The lower seed, lying nearer the base of the bur, 
is concave on the outer face and convex on the inner, ARTHUR 
found that plantings of burs of the cocklebur (mainly Xanthium 
canadense) in a garden bed resulted in 
the germination of all the lower seeds 
in the first year after ripening, and 
of only a very small per cent. of the 
upper seeds, The second year a 
teat majority of the upper seeds 
grew. A few of the upper ones, how- 
ever, grew in the third and fourth years. 
MAasTERMAN (7) claims that both 
seeds grow the first year after they 
are planted. His methods, however, 
Were not at all adapted for detecting 
whether the two seeds of the bur have 
markedly different germinative char- 
acters. Both Arruur’s work and 
the experimental results of this paper Fic. 1.—Cocklebur cut away to 
show that such differences in the ger- show upper and lower (dimorphic) 
minative characters undoubtedly exist. — 
Delayed germination was found by Nopse and HANLEIN to be 
due in many cases to the impermeability of the seed coat to water. 
As to the seeds listed in Table I, however, they say that in every 
case the seeds absorbed the water readily and yet lay in the germi- 
nator in a saturated condition for long periods, either not germinating 
at all or scattering their germination over a long period. They main- 
tain that in cases where water is admitted the growth after long 
“Xposure to germinative conditions must be due to some change going 
on within the embryo during the period of rest. WINKLER (15), 
WIESNER (14), Krenirz (4), and Prerrer (9) expressed similar 
views, 
ARTHUR found that both seeds of the cocklebur take up water 
Teadily while in the bur. The bur, therefore, does not account for 
the delay. He also believes that the extremely delicate seed coats 
‘re in no way different in the two seeds and that the structure of the 
Seeds, therefore, offers no explanation of their germinative difference. 
