362 PLANT LIFE. 



The methods by which distribution is secured may be 



grouped as follows : 



490. 1 . Distribution by tension and turgor. — Some plants 

 (e.g., witch hazel) as they ripen the pericarp, alter its tissues 

 in such a way that the contained seeds are compressed when 

 the pericarp dries, and after it opens they are pinched out 

 from the narrowing 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 peri- 

 carp shorten on one side until the strain breaks them loose, 

 when they become suddenly elastically curled and sling 

 the seeds contained to a considerable distance (fig. 405). 

 Somewhat similar causes, i.e., curvatures due to unequal 

 shrinkage or swelling of the tissues, enable some fruits 

 with long awn or bristles to creep over the ground or to 

 bury themselves in it when al- 

 ternately moistened and dried 

 (fig. 406). The pericarp of the 

 squirting cucumber is so dis- 

 tended by the almost liquid 

 pulp surrounding the seeds that 

 it ejects the mass through the 

 opening formed by its separa- 

 tion from the axis. 



491. 2. Distribution by 

 water. — In some plants this 

 is secured by the fact that the 

 fruits open only when moist- 

 ened. In such cases the seeds .. , _. ..,.,. 



lie 406.— Pieces mli> which the fruit of 



may be either Washed OUt from storksbill breaks. There are five ol 



J these each corresponding to .1 carpel and 



the opening pods by rain, or arranged on the sides <.i a prolonged 



1 ° ' - torus as in A , fig 405. A, when dry the 



may be loosened in many beak is spiraHy .-..iie.!: a, when moist. 



' - I lie l>asc is hard and very slurp. .Magin- 



other ways. The seeds are Bed about a diam.— After Noll. 



thus set free at the time best suited to their prompt germi- 



