IOWA ACADEMY OP SCIENCE 
21 
of germination and lessen the dormant period, especially true of seeds 
with hard coats; where the coats were thin the dormant period was 
still less than with hard coated seeds. For instance the dormant period 
of common Pig Weed {Amarantus retroflexus) was nine and one-third 
days when kept in packages in a dry room and only six and one-third 
days after having wintered out of doors. In the case of Wild Rye, the 
dormant period was lessened from nine to five days. In the common 
Foxtail {Setaria glauca) the average dormant period was lessened from 
eleven to seven and one-fourth days and the percentage of germination 
from 34.5 per cent to 38 per cent, while the percentage of germination 
in the Wild Rye was increased from 22 per cent to 48 per cent and 
the Pig Weed increased from 40 per cent to 50 per cent. In general, 
the longest dormant period was found in those seeds which have the 
hardest and thickest seed coats. The longest dormant period for the 
Great Ragweed was 152 days; the Barn-yard Grass, 178 days. In this 
connection it is also interesting to observe that the highest percentage 
of germination for any planting was the common Mustard {Brassica 
arvensis) which was 100 and for the six plantings, 90.3 per cent. 
It has been known for a long time that many seeds refuse to germi- 
nate until they have passed a period of rest; Dr. MacDougaT calls at- 
tention to an interesting condition observed in Arizona in regard to 
some of the annual plants in which delayed germination occurs. Nobbe 
and Hanlein.^ who made a study of the weed seeds of thirty-one dif- 
ferent species and continued their experiments for 1,173 days, found 
a number of these weeds showed germination after a lapse of 1,173 
days and among them were Campamila persicifolia; Ghelidomum majus; 
Mysosuriis minimus; Plantago media; Potentilla argentea and Thlaspi 
arvense. 
WinkleF observes that the seeds of Euphorbia Cyparissias though 
planted in the spring did not germinate in some cases until forty years 
later. He states also, that the seeds of Malva moschata will not germi- 
nate in the season of their production. 
Wiesner® states in some cases nine years are required for the germina- 
tion of Euphorbia exigua. He notes, also, the well-known fact that in 
the case of Red Clover Trifolium pratense, some seeds will germinate the 
^The Course of the Vegetation in Southern Arizona. Plant World Nov., 1908. 
Separate 13. 
^Ueber die Resistenz von Samen gegen die ausseren Factoren der Keimung. 
Landw. Versuchs-Stat. 20:63-96. 1877; the original of this paper was not 
available, the facts are taken from Crocker. Hanlein, Ueber die Keimkraft von 
Unkrautsamen. Landw. Versuchs-Stat. 25:465-470. 1880. 
^Bermerkungen uber die Keimpflanzen und die Keimfahigkeit des Samen von 
Tithymalus Cyparissias. Ber Deutsch. Bot. Gesells. 1:452-455. 1883. 
