Apr. 15. 1921 
Susceptibility of Injured Seeds to Molds 
101 
experiments were conducted to determine the relation of viability and 
vitality of the wheat to susceptibility to Penicillium and Rhizopus. 
Perfect seeds were killed both by boiling for one minute, after which 
they were dried, and by prolonged exposure to a saturated solution of 
copper sulphate. The coats of some of these seeds were then broken 
over the embryo, some were broken over the endosperm, and others were 
left uninjured. Lots similarly treated were placed in the laboratory 
and in the refrigerator, those in the latter being removed after a week. 
Blotters sprinkled with spores of both Penicillium and Rhizopus were 
used. The results showed that, under all conditions of injury and of tern- 
perature, the dead seeds were attacked by both fungi, except that Rhizo¬ 
pus did not attack any seeds killed by copper sulphate. Penicillium is 
less sensitive to this chemical and therefore was much in evidence as 
green tufts of mycelium growing in the ruptures over both endosperm 
and embryo and spreading more thinly over the entire area of the 
unbroken seeds. Invariably, however, the latter were attacked more 
slowly and showed less abundant mycelium than those with seed coats 
broken. From this we conclude that the testa still was a considerable 
barrier to the invading hyphae. 
Striking illustrations of the fact that seeds otherwise immune became 
very susceptible to attack by saprophytes when weakened or killed by 
treatment were afforded by many blotter germinations in connection 
with experiments on formaldehyde injury. It was found, in a series of 
lots of seed stored in atmospheres of progressively increasing humidity, 
that a point was reached where paraformaldehyde did not form upon 
the evaporation of formaldehyde, and at approximately that point the 
stored wheat ceased to show injury. The development of Rhizopus in 
the blotter germinations of these lots was found to furnish a good index 
of the amount of injury sustained by the samples, as it developed most 
quickly and luxuriantly on the worst injured samples, decreasing in 
amount until there was practically no mycelium on the uninjured seeds. 
Experiments demonstrating that seed stored damp was uninjured by 
the 1 to 320 formaldehyde treatment, 1 while that allowed to dry under 
certain conditions suffered serious injury, showed this same relation¬ 
ship between viability and susceptibility to Rhizopus (13). The injured, 
dry-storage seeds were always more or less covered with Rhizopus 
mycelium, while the uninjured, damp-storage seeds remained clean (PI. 
19). The same results were obtained in experiments to show that wash¬ 
ing with water after treatment removed the danger of formaldehyde 
injury on the drying of the seeds. The unwashed, injured seeds were 
severely attacked, while the washed, uninjured seeds were attacked but 
slightly, if at all (PI. 20). 
1 The strength of formaldehyde solution used in seed treatment for smut is i pint of commercial formalde¬ 
hyde in 40 gallons of water. The corresponding solutions used in this investigation consisted of i part of 
commercial formaldehyde in 320 parts. Since the commercial formaldehyde solution contained 36.2 per 
cent of formaldehyde gas,this dilution would be one part o formaldehyde in 884. ora o.iij per cent solution. 
