THE VIABILITY OF RADISH SEEDS 
301 
tures. Other investigators of this early period obtained similar results. 
More recently, Jodin (1899) found that seeds of peas and cress 
when dried at 60° C. for twenty-four hours can be heated at 98° C. 
in the dry air of sealed tubes for six hours and still retain their viability ; 
similar seeds heated in humid air at 40° C. lost their viability in twenty 
hours. In subsequent experiments he found that the resistance of 
the seeds of pea and cress was increased in a marked degree when 
calcium chloride was introduced into the tube with the seeds. He 
states that seeds may be exposed to dry air at 65° C. for prolonged 
periods without loss of vitality, but adds that this may be done only 
if one heats them in an open dish to permit a rapid loss of water from 
the seeds. If the air becomes saturated with water vapor, the seeds 
can endure only a comparatively low temperature without injury. 
Dixon (1902) dried various kinds of seeds over sulphuric acid and 
later in an oven at 95° C. for several days without destroying their 
viability. He treated the samples in closed test tubes and found that 
when sufficiently dry the seeds could withstand temperatures far 
above that of boiling water (110° C.-i2o° C.) without injury. Neu- 
berger (1914) and others of recent date, in their studies on the com- 
parative resistance of moist and dry seeds to high temperatures, in 
a general way, confirm the results of the earlier authors. 
Pouchet (1866), working with seeds of Medicago obtained from 
sheep-wool brought from South America, found that they germinated 
after being exposed to boiling water for four hours. He subsequently 
experimented with other Medicago seeds and found that only those 
germinated which, after a prolonged treatment in boiling water, did 
not swell. Nobbe (1876) confirmed Pouchet's results. Dixon (1901) 
and Schneider-Orelli (1909, 1910) attributed the high resistance of 
these seeds to the fact that many of the seed coats are impermeable 
to water. 
From the above review, it is apparent that considerable work has 
been done on the resistance of seeds to high temperatures. The 
experiments have been carried on with seeds containing widely different 
and undetermined amounts of water. As far as the writer has been 
able to determine no one has attempted to study, in series, the resist- 
ance of the same kind of seeds containing definite and known quan- 
tities of water at the time of heating. It is only through a quantitative 
study of this kind that a definite knowledge of the various factors 
involved can be obtained, and the variation in results harmonized. 
