WOOD SORREL 135 



that the starchy layer impels the seed by its expansion, 

 but there is reason to believe that this is not so. The 

 elastic layer does really contract, and often breaks up 

 in doing so. The supposed expansion of the starchy layer 

 would imply turgidity or distention by water, but the seed 

 goes oft in alcohol, salt solution, and other liquids which 

 strongly absorb water. Instead of the starchy layer 

 swelling, while the elastic layer is passive, it is more likely 



FIG. 36. Section of outer tissues of wood 

 sorrel seed, deh, dehiscing layer, along which 

 the separation takes place ; the other letters as 

 in Fig. 35. 



that the elastic layer contracts, while the starchy layer is 

 passive. 1 



A yellow-flowered wood sorrel (Oxalis corniculata) is 

 remarkable for its world-wide distribution ; it is absent 

 only from the coldest regions. Perhaps it owes its almost 

 universal dissemination in some measure to its singular 

 power of scattering its seeds. The yellow wood sorrel 

 flourishes as a weed in many gardens and greenhouses, 



1 I have to thank Mr. T. H. Taylor for these observations on the 

 elastic layer. 



