256 A TEXT-BOOK OF BOTANY 
sling-fruits. In the violet and the witch-hazel, when the 
seed-vessel splits, its walls press upon the seeds so that they 
are pinched out, as a moist apple-seed is projected by being 
pressed between the thumb and the finger (Fig. 248). 
When the pod of the wild bean bursts, the two valves twist 
violently and throw 
the seeds (Fig. 249). 
In the touch-me- 
not, or the balsam, 
a strain is devel- 
oped in the grow- 
ing wall of the 
seed-vessel, so that 
at rupture, which 
may be brought 
Fic. 250.—Winged fruit of maple.—After KERNER. about by slight 
pressure, the pieces 
suddenly curl up and throw the seeds. The squirting 
cucumber is so named because it becomes very much 
distended with water, which is finally forcibly ejected 
Fic. 251.—Winged seed of Bignonia.—After STRASBURGER. 
along with the mass of seed. In tropical forests there 
are plants whose large seed-vessels explode with a loud 
report. 
