68 
N. C. Experiment Station 
A number of investigators have shown that the permeability of cellular 
membranes to gases depends upon their state of humidity. Becquerel* 
working with lupin, pea, and bean (Faba) found that their seed coats 
in an air dry condition are impermeable in all their parts to dry air, but 
when the same seeds are exposed to an atmosphere saturated with water 
vapor, the integuments imbibe sufficient moisture to permit the slow 
passage of gases. No one has studied the permeability of the testas of 
cotton seeds to hydrogen and carbon dioxide but the work of Becquerel and 
others indicates that the permeability decreases with increasing desiccation 
and may actually become nil at the degree of dryness attained when seeds 
are stored under laboratory conditions. While no moisture determinations 
were made on the seeds used in the writer’s tests described above, it is 
known that the seeds in Experiments 1 and 2 in which the amount of 
anthracnose was markedly reduced in the treated lots, were stored in the 
gases very soon after their arrival at the laboratory. On the other hand, 
the seeds used in Experiments 3, 4, 5, and 6 in which less reduction of 
anthracnose occurred, remained for a considerable time in the dry air of 
the laboratory before the experiments were started and may have become, 
by reason of more thorough desiccation, less permeable to the gases in 
which they were kept. 
The only conclusion that can safely be drawn from these experiments 
is that storage in C0 2 and H 2 cannot be relied upon to free cotton seeds from 
infection by the anthracnose fungus. This agrees with the finding of Barre 
and Ludwig, 3 who reported that storage of infected cotton in gases did 
not free the seed from the anthracnose disease. 
GENERAL CONCLUSIONS 
In order to enable cotton seeds to withstand, without loss of viability, 
the high temperatures to which they must be subjected in the final stages 
of the dry heat treatment for anthracnose, it is essential that their water 
content be reduced to a small fraction of that which is commonly found 
in seeds stored under ordinary conditions. This preliminary desiccation 
can be accomplished conveniently and most rapidly by drying the seeds at 
a temperature too low to harm them. The degree of dehydration required 
varies in direct manner with the temperature which is to be used in 
the final stages of the treatment and is fully attained by reducing the 
water content of seeds which are to be heated for 12 hours at 95° to a 
value which is equivalent to 3.2 per cent of their air dry weight. Both 
the temperature and the time of drying are factors of primary significance 
in this operation. If the temperature is too low, the time of drying can 
be extended indefinitely without accomplishing the desired degree of desic¬ 
cation. The absorptive power of the dry air comes into equilibrium with 
the hydrophyllic properties of the colloids and other constituents of the 
living cells of the seed before the state of desiccation which will enable 
the seed to survive high temperatures has been reached. On the other hand, 
when a temperature which is sufficiently high is used, a more or less definite 
minimum of time is necessary to produce a degree of desiccation sufficiently 
pronounced to protect the seeds. A temperature of 45° C. cannot produce 
