1906] CROCKER—DELAVED GERMINATION 289 
the bur, and that it is impossible to have the two seeds distributed 
in space, so a distribution in time is substituted. Why such an inde- 
hiscent involucral structure should be developed instead of such a 
bur as appears in the burdock needs answer. With the indehiscent 
bur already in existence the advantage is plain. It is clear that such 
germinative characters as appear in the seeds of Axyris amaran- 
thoides, Abutilon Avicennae, etc., insure that the soil will always be 
supplied with these seeds in process of germination. The destruc- 
tion of existing vegetation, by fire or otherwise, is followed by a 
quick appearance of these weeds. In species where none of a given 
crop of seeds grow until a year or more after falling, it would seem 
that the adaptive characters, if they be such at all, had overstepped 
the line of greatest advantage. 
V. Summary. 
1. Delayed germination is reported in the seeds of many plants 
and, exactly Opposite to the common view, its cause generally lies 
in the seed coats rather than in the embryos; but in the hawthorns, 
as perhaps in some other seeds, it is due to embryo characters. 
2. In the upper seed of the cocklebur the delay is secured by the 
seed coat excluding oxygen, while in Axyris amaranthoides, Abutilon 
Avicennae, and many other seeds, it is secured by the coats excluding 
water. 
3. In Iris seeds the failure to germinate is due to the endosperm 
and cap stopping water absorption before the quantity necessary for 
germination is obtained by the embryo. 3 
4. In Plantago major, P. Rugelii, Thlaspi arvense, Avena jatua, 
and others, the real method by which the coats secure the delay is 
hot yet determined, but there is no doubt that the delay is due to 
the coats, 
5. Seed coats which exclude water are much better adapted to 
securing delays than are seed coats which exclude oxygen, because 
of the much greater reduction of respiration in the first case. 
6. In nature growth of the delayed seeds comes about through 
the disintegration of the seed coat structures by a longer or shorter 
exposure to germinative conditions, and the length of the delay 
depends upon the persistence of the structure securing it. 
