314 SEMI-CENTENNIAL OF TORREY BOTANICAL CLUB 
Two collections of leaves from the same host tree were made. 
The results are in excellent agreement. 
Phoradendron macrophyllum on Populus 
Four determinations on Populus Wislizenii (S. Wats.) Sarg. 
were secured from two large trees, 4-5 feet in diameter, on the 
banks of the Rio Rillito, August 12. 
Coll. 532, Parasite 1, Ac 1.06, Е 223.6 
FOZ 4.43 
Parasite 2, A = т.91,-Р = 229 
+ 0.30, + 3.6 
For host, A = 1.61, P = 19.3 
The leaves of the host were taken as near as possible to 
Parasite I. 
Coll. 533, Parasite 1, А = 1.04, Р =-23.3 
For host, A = 1.79, P = 21.5 +0.15, + 1.8 
Parasite 2, A = 2.13, P = 25.6 
For host, A = 1.76, P = 21.2 + 0.37, + 44 
The two samples of the leaves of the host were taken as near 
as possible to the parasites with which they are compared. 
III. DISCUSSION OF CONSTANTS 
Taking the results for the broad-leaved Phoradendron, P. 
macrophyllum and P. macrophyllum Jonesii, on Fraxinus, the data 
show that in both of the two determinations made in the early 
spring the osmotic concentration of the tissue fluids of the parasite 
was considerably higher than that of its host plant. 
The average of the two determinations is 29.05 atmospheres 
for the parasite as compared with 18.15 atmospheres for the host, 
or an average difference of 10.90 atmospheres. 
In the summer collections, the data show that there are eight 
cases in which the osmotic concentration of the parasite is higher 
than that of the host as compared with three cases in which it is 
lower.* 
* The results for one determination (Coll. 520) are not included because the only 
trustworthy value for the host was obtained on a different date. Two of these 
of the parasite were definitely noted as old. The third exception (Coll. 576) came in 
a series in which four samples were taken from a partly dead tree. Possibly this one 
of the four plants was not in a normal condition. 
