182 T. Holm — Dirca Palustris. 



in the living plant. With reference to the crystals of cal- 

 cinm-oxalate Van Tieghem credits the occurrence of 

 styloids to Dirca, which evidently depends on an error, 

 since this type of crystals was not found in any parts of 

 the plant, although I had ample material for comparison. 



Considering the fact that Dirca palustris is an inhab- 

 itant of damp, rich woods, and that the material, which I 

 have examined came from shaded places in woods on the 

 Potomac shore, the structure is somewhat anomalous. 

 For sciaphilous plants are not, as a rule, equipped with 

 such abundance of mechanical tissue as is the case of 

 Dirca. The bark of the root and stem is so tough, that it 

 is used in many parts of the country for ropes, a practice 

 borrowed from the Indian tribes ; this peculiar character 

 is expressed by some of the popular names, viz : Leather- 

 wood, Ropebark, and Bois de plomb in Canada. More- 

 over the structure of the stomata, being confined to the 

 lower face of the leaf, and being sunk below the epidermis, 

 is a heliophilous rather than a sciaphilous structure. 



The internal structure of Dirca thus illustrates one of 

 the numerous cases, where the anatomical characters can- 

 not be brought in correlation with the surrounding 

 medium, and may be explained most probably as simply 

 inherited characters.* 



Clinton, Md., March, 1921. 



* Compare Vesque, J : De 1 'anatomie des tissus applique a la classification 

 des plantes, Nouv. Archiv. du Museum d 'hist, nat, Ser. II, vol. 4. 



