1879. ] Seeds of Plants as Projectiles. 95 
form of a hooded scale. Achenium ovate, compressed, straight 
and erect, partly or nearly naked.” 
In P. pumila the distal end of the elastic hooded scales are 
held down by the otherwise naked seed. The rudimentary 
stamens may be compared to a V-shaped spring, the ends of 
which are pressed together. When the seed is ripe and its con- 
nection with the receptacle broken, the hooded scales suddenly, 
partially straightens and the seed shot into the air five feet or 
more. The arrow-head shape of the achenium, and the arrange- 
ment of the cymes on long axillary stems shortened from below 
upwards, are favorable to the great range of the flying projectile. 
The mechanism of the movement is sufficiently simple, but the 
special adaptation of an essential organ of a perfect flower toa 
new use is very peculiar. 
Prof. Gray says of Oxa/is: “ Pod membranaceous, deeply five 
_ lobed, five celled, each cell opening on the back. Seeds few in 
each cell, pendulous from the axis, their outer coat loose and sep- 
arating.” The loose outer coat of the seed of Oxalis stricta 
bursts on the edge opposite its attachment to the axis, and 
is suddenly rolled back, breaking the funiculus, and at the same 
time separating the walls of the cell and projecting the seed two 
or three feet. By this movement the loose coat is generally 
turned inside out. The flattened oval seeds are marked on their 
sides by transverse striz that doubtless give direction to the elas- 
tic coat when it bursts. Before the seeds are fully matured they 
may be removed from the cell and the coating caused to burst by 
touching them with some sharp-pointed instrument. So quick is 
the movement that one is strongly reminded by it of a jens 
flea. No other species than Oxalis stricta was observed. 
That the movements of the seeds described are important, if 
not essential to the life of the plant, seems evident. The ripening 
capsules of the violet may be found until late in autumn, we have 
seen them after snowfall, and without some such movement as © 
has been mentioned, would go on seeding the same ground 
the season through, and year after year. The same remark is true 
of the wood sorrell, the membranaceous pod of which would other- 
wise fall to the ground near the root of the plant carrying its 
crop of seeds with it. The general resemblance in habit and 
appearance of balsam and richweed would lead us to expect some 
special provision for scattering their seeds in the one as the other. 
