1906] CROCKER—DELAYED GERMINATION 285 
IV. General considerations. 
Two statements of ARTHUR concerning the cocklebur need special 
consideration. He says: ‘Seeds in the bur retain their germinative 
power, when kept in a dry room, for two years or more; but seeds 
removed from the bur dry out within a few days and will no longer 
grow. Seeds removed from the bur and placed in a germinator retain 
their bright polished appearance as long as they are alive; when dead 
they turn dull and lusterless.” I find that the seeds retain their 
vitality fully as well when removed from the bur and allowed to dry 
as when in the bur. In fact, a dry cool place is the best for storage 
of these seeds whether in or out of the bur, as is true for most seeds. 
The seeds removed from the bur and kept in a dry place retain their 
vitality much more than five years. I found the condition of the 
seed coat no indicator of the vitality of the embryo. The coat through 
disintegration loses its luster and turns black or sometimes colorless, 
which means that more oxygen is admitted and that the minimum 
germinative temperature of the seed has fallen. It is not surprising 
that ARTHUR drew these conclusions, for his work gave him no idea 
of the germinative conditions of the upper seeds or of the significance 
of the seed coat, 
As Duvet (3@) states, seeds retain their vitality longest in condi- 
tions that permit of least respiration. KoLKwiTz (5) has shown that 
respiration is extremely slight in dry seeds at low temperatures. 
The embryos of seeds whose germination is delayed by coats that 
exclude oxygen, such as Abutilon, Axyris, and Chenopodium, are 
kept very dry by the coats. As they lie in the ground they are like- 
wise relatively cool. In nature, in short, they have the most favor- 
able storage conditions up to the time when the coats, through partial 
decay or long exposure to water, admit moisture and germination 
begins. It is not wonderful that such seeds lie in the ground twenty 
'o twenty-five years and yet retain their vitality. While the reduction 
in the oxygen admitted to the upper seed of the cocklebur cuts down 
the respiration considerably, it does it to no such extent as does the 
exclusion of water. The coats that exclude water are undoubtedly 
much better ada pted to securing a long delay than are the coats that 
merely exclude oxygen. In nature the longer delays are certainly 
secured by the former method. 
