The Anatomy of Phoradendron villosum Nutt. 



By W. A. Cannon 

 (With Plates 27, 28) 



The California species of the American mistletoe (P. villosum), 

 in the vicinity of Stanford University, is found on several kinds of 

 evergreen and deciduous trees, among which are the following : 

 Common locust (Robinia pseudacacid), Lombardy poplar (Populus 

 nigra), species of willow, and the Roble, Douglas, Encina, and 

 Kellogg oaks {Quercus lobata, Q. Douglasii, Q. agrifolia and Q. 

 Kelloggii) and it has been reported from Chico, California, as oc- 

 curring on the cultivated peach. The parasite is abundant on the 

 Roble oak, and since the latter is common in the vicinity of the 

 university, it was chosen to study as the host. 



The present paper deals merely with the anatomy of the mistle- 

 toe, but it is intended that it shall be followed as soon as convenient 

 by a contribution from the Botanical Laboratory on the biology of 

 the plant. 



. The material was collected mainly in the spring and early sum- 

 mer of 1899. It was killed with alcoholic corrosive sublimate, 

 and all of the sections were cut by hand. 



This study was carried on under the direction of Dr. G. J. 

 Peirce, to whom I take pleasure in expressing my gratitude for his 

 great helpfulness in this, and in other work. 



1. The Leaf 



The leaves of the mistletoe are borne in alternating pairs on 

 stout stems, which arise from the host at varying angles in respect 

 to the horizon, and consequently in reacting to the light, the leaves 

 assume a more or less vertical position and become bent in petiole 

 and blade. They are relatively thick, of a yellowish-green color, 

 and are markedly brittle. There is a regular gradation in the size 

 of the leaves throughout the younger portion of the plant, so that 

 it is impossible to assign most of them to a definite season's growth. 

 The mature ones measure 3.25-4 cm. in length by 2.5 cm. in 



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