Randolph : Influence of moisture upon ivy 99 



tion with the tropical vines which send down roots to the soil from 

 different points along the climbing stem. These roots (Nahrwurzel) 

 convey to the upper parts of the vines a supply of water for which 

 their thin stems are wholly inadequate.* Roots of this kind arising 

 from the stem are believed to have their phylogenetic origin from 

 holdfast-roots (Haftwurzel).f The roots that now grow out from 

 the holdfast-roots of the ivy may represent an early stage of this 

 process. The presence of large numbers of root-hairs is evidence 

 that these secondary roots that spring from the stem have the func- 

 tion of absorption. As in the case of the tropical vines, J there is 

 in the ivy a difference in structure between the absorptive roots 

 and the holdfast-roots. 



The presence of secondary absorptive roots in the ivy brings this 

 species into closer relation with other members of its family (Ara- 

 liaceae) in the tropics, and with epiphytes in general. Schenck 

 states: "In fast alien Familien oder Gattungen mit wurzelklettern- 

 den Lianen begegnen uns gleichzeitig auch epiphytische Formen. 

 So enthalten die Araliaceen in den Tropen epiphytische Holzge- 

 wachse. . . . Wurzelkletterer und Epiphyten sind verwandte Veg- 

 etationsformen, und aus ersteren konnen sich leicht letztere her- 

 ausbilden, falls die Verbreitungsmittel der Fruchte oder Samen 

 entsprechende sind. ... In der That giebt es ja auch viele krei- 

 chende oder wurzelkletternde Epiphyten, welche in manchen 

 Eigenthumlichkeiten mit den echten Wurzelkletterern iiber- 



einstimmen. 



ft 



Bryn Mawr College. 



* Schenck, loc. cit. 106. 



fGoEBEL, K. Organographie der Pflanzen 4S8. 1900 

 % Goebel, loc. cit. 487. 

 $ Loc. cit. in. 



