278 



OUTLINES OF PLANT LIFE. 



scattering the seeds, which contain the young plants in a 

 dormant condition. 



The methods by which distribution is secured may be 

 grouped as follows : 



396. I . Distribution by tension and turgor. — Some plants 

 (e.g., witch hazel) as they ripen the seed vessel, alter its tis- 

 sues in such a way that the contained seeds are compressed as 



Fig. 240. — Elastic valves for slinging seeds. A^ fruit of wild geranium {G. palustre) 

 with persistent calyx. The five carpels surround an elongated torus, from which they 

 break first at bottom; curling upward suddenly they sling the seed out of .the basal 

 part which has cracked along the inner side. B, fruit of touch-me-not {Im^aiiens 

 noli-tne tangere)^ one sound, the other bursted. The carpels have curled up elasti- 

 cally from the base and slung out the seeds. Natural "size. — After Kerner, 



it dries, and after it opens they are pinched out from the nar- 

 rowing valves, as a wet apple or melon seed may be shot from 

 between the thumb and finger. In others (e.g., touch-me- 

 not and cranesbill) the parts of the seed pod shorten on one 

 side until the strain breaks them loose, when they suddenly 

 become elastically curled and sling the seeds contained to a 

 considerable distance (fig. 240). Somewhat similar causes, 

 i.e., curvatures due to unequal shrinkage or swelling of the 

 parts, enable some fruits with long awns or bristles to creep 



