376 Cannon : Anatomy of Phoradendron villosum Nutt. 



siderably sunken beneath the surface they are less so than those 



of the stem. In comparing the stomates of the mistletoe with those 



of the oak in regard to size and number, it is found that those of 



the former are about twice as large (Fig. 2) and only approximately 



half as many to a given area as those of the latter. The number of 



stomates per square millimeter on each surface of the mistletoe 



leaf is about 40, while on the oak, where they occur on one side 



only, there are about 80. 



The conductive system of the leaf is poorly developed and the 



tracheids at the ends of the leaf traces are not swollen as in Lor- 



anthus, and to some extent in Viscum* No water reservoirs, such 



as are described by Marktanner-Turneretscher for Viscum, the 



presence of which is denied by Solereder, f are to be found in P. 

 villosum. 



The color given to the mistletoe by the cuticle, which was 



» 



spoken of above, has led to a supposition that there is a peculiar 

 quality of chlorophyll in the plant that is in some manner asso- 

 ciated with its parasitic habit. This is not at all the case. 

 The external color of the plant is entirely due to the coloration of 

 the cuticle, and the chlorophyll, as far as I could determine, 

 was quite normal. I tried to dissolve out the coloring matter 

 from the cuticle by using the common solvents and thus learn its 

 nature, but in this I was quite unsuccessful. 



The leaf of the mistletoe is mechanically very weak. This is 

 partly due to the poor development of supporting tissue, but 

 chiefly to the prominent intercellular spaces. If a leaf is broken ' 

 in two, and sections are cut at right angles to the fracture, it will 

 be seen that the line of fracture passes between the cells, or that, 

 in other words, it coincides with the intercellular spaces. It is 

 likely here as in the stem that perhaps the main element of 

 strength lies in the unusual development of the outer epidermal 

 wall, the cuticle. This will be spoken of again later in this paper. 



2. The Stem 



A cross section of a young stem shows a wood cylinder made 

 up as usual of conductive tissue, medullary rays, wood paren- 



* Marktanner-Turneretscher, 1. c. 



t Solereder, Anatoraie der Dicotyledonen. 



