396 



ECOLOG V. 



horizontal root, and possess a fancied resemblance to a knee. 

 These knees are said to occur at points on the horizontal root 

 above and opposite the point where a root branch extends down- 

 ward into the soft marsh soil. They thus give strength to the 



Fig. 490. 

 Cypress knees, Mississippi. (Photograph by H. von Schrenk.) 



horizontal root at the point of attachment of the branch which 

 penetrates into the soft soil, and during gales they hold these 

 root branches more rigidly in position than would be the case if 

 the horizontal root could easily bend at this point. The knees 

 thus are supposed by some to strengthen the anchor formed by 

 the root in the loose soil. Their development maybe the result 

 of mechanical irritation at these points on the horizontal root, 



