Cannon: Anatomy of Phoradendron villosum Nutt. 389 



sinkers that have severed their connection with the main part of the 

 parasite through the death of the cortical haustoria, so choke the 

 passages of the host's conductive system that growth ceases and 

 it eventually dies from starvation.* In the American mistletoe, on 

 the other hand, the destruction of the host tissues is brought about 

 by the living sinkers which, while still attached to the cortical, now 

 become the aerial haustoria, occupy the places of the medullary 

 rays (Fig. 8) and absorb so much water that the more distal por- 

 tions of the host are starved. The position which the American 

 mistletoe often occupies at the extreme tip of a limb is brought 

 about in the manner described with the further note that the para- 

 site may extend its haustoria to include within its grasp the branch 

 of which the one on which it germinated was an offshoot (Fig. 7). 



Columbia University, March 13, 1901. 



Explanation of Plates 



Plate 27 



1. A cross section of a leaf the same age as the leaf of Fig. 4, showing a 

 stomate, X 22 °- 



- 



2. Surface view of stomata to show the relative size : 0, oak, Af, mistletoe, 

 X 220. 



3. A cross section made in April of a leaf of the first season : D, dorsal surface, 

 K ventral surface, X 7^. 



4. A cross section of a leaf of the second season made in the spring before the 

 growth in diameter was completed. A few cells with calcium oxalate are shown, X 7*>. 



5- A cross section of a stem of the same age as that of the following figure, with 

 a characteristic sunken stomate, X 22 °' 



. 6. A section of a rather young stem showing the great development of cuticle, 



X 320. 



7. Oak branch and mistletoe attached : m, mistletoe ; Ae, aerial haustorium ; b, 

 the branch upon which the mistletoe germinated, the end of which is indicated by the 

 dotted lines. Two thirds natural size. 



8. A cross section of an oak branch with a mistletoe. The cortical haustoria have 

 surrounded the wood cylinder of the oak, and sinkers penetrate it from every side ; 5, 

 sinkers, X ("*) 2. 



Plate 28 



9. A section through the epithelial region of a cortical haustorium ; P, parasite ; 

 &> host, X 22 Q. 



* Frank, /. c. 



