ROLE OF SEED COATS IN DELAYED GERMINATION. 
CONTRIBUTIONS FROM THE HULL BOTANICAL LABORATORY. 
WILLIAM CROCKER. 
(WITH FOUR FIGURES) 
I. Historical. 
Ir is well known that in many species of plants not all the seeds 
of a given crop germinate promptly after being subjected to so-called 
germination conditions; instead they germinate at irregular inter- 
vals through a period of weeks, months, or even years. It happens 
in many species that none of the seeds of a crop will germinate until 
they have been subjected to germinative conditions for a year or 
more, and that in these cases of marked delay germination is dis- 
tributed through a further period of greater or less length. 
Delayed germination is well illustrated in the results of the 
researches of NoBBE and HANLEIN (8, a, b). Table I shows their 
observations on thirty-one species of common weeds, They began 
With 4oo seeds of each species and continued their experiments 1,173 
days, 
Krenitz (4) found marked distribution in the germination of 
crops of the beech, white fir, ash, hornbean, and pine; and WINKLER 
(15) in sowings of Euphorbia cyparissias, E. exigua, Cuscuta, etc. 
WIESNER (14) found that the seeds of Viscum album germinate only 
sparingly in the fall after ripening, but readily the following spring. 
Kuntze (6) in reviewing the literature on germination mentions a 
large number of cases of delayed germination. The hawthorn, he 
states, will grow only after being in the ground one to three years. 
One of the most interesting cases of delayed germination is that 
of the cocklebur (Xanthium) reported by ARTHUR (Ty. ac found 
that the two seeds in the bur are not the exact counterparts of each 
other, but can be distinguished readily by their form and position in 
the bur. One seed, which he terms the upper because it is borne 
nearer the apical end of the bur, is convex on the outer face and con- 
265] [Botanical Gazette, vol. 42 
