362 



PLANT LIFE. 



The methods liy whicli distribution is secured may be 

 grouped as follow's : 



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

 (e.g., witch ha/cl) as tlicy ripen the pericarp, alter its tissues 

 in such a wav that the contained seeds are compressed when 

 the pericarp dries, and after it opens the)' are pinched out 

 tVom the narrowi;ig 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 tlie jjcri- 

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

 when they become suddenh' elastic alh' curled and sling 

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

 Somewhat similar causes, i.e., curx'atures due Xo uneipial 

 shrinkage or swelling of the tissues, enalile some Iruits 

 with long awn or Ijristles to creep o\'er the groiuid or to 

 Viurv th.emseb'cs in it when al- 

 ternately moistened and dried 

 (fig. 406). The ]iericarp of the 

 S(|uirting ( ucumbcr is so dis- 

 tended by the almost' liipiid 

 pulj) surrouiidiiig the seeds that 

 it ejects the mass through the 

 0|icning 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 wlien moist- 

 ened. In such cases the seeds 

 may be either washed out fVoni 

 the opening pods by rain, or 

 may be loosened in many 

 other ways. The seeds are 

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



A 



-I'i 



iUi> wliicli llie fviiil iif 

 storksbill breaks. 'I'licre are ti\e cit" 

 tliese eacli corresponding to a carpel and 

 arranged on the sides of a prolonged 

 lorus as in .-/.fig. 405. A, wlien dry "the 

 heak is spirally coiled: />', when moist. 

 The base is hard and \"ery sbaip. I\Iagni- 

 lied about 2 diam -.After Noll. 



