Harris: DESERT LORANTHACEAE 309 
conclusion against data from as widely dissimilar environmental 
conditions as possible. 
II. PRESENTATION OF DATA 
Since earlier studies have shown that in trees the concentra- 
tion of leap sap is related to the height of insertion of the leaves,* 
care was taken in the collection of samples of the host leaves to 
secure them from as nearly as possible the same level as the 
parasite. Generally they were gathered from the same branch. 
Osmotic concentration was measured by the cryoscopic method. 
Sap was extracted after freezing] the tissues to obviate the dif- 
ferential extraction of sap, first carefully investigated by Dixon 
and Atkinst and verified by ourselves.§ 
The results are expressed in terms of freezing-point lowering in 
degrees centigrade, corrected for undercooling| and in atmos- 
pheres pressure from a published table. f 
The actual constants for parasite and host, together with the 
habitats of the species and the dates of the determinations, are 
given below. 
The original collection numbers are retained. The values at 
the extreme right are the constants for the parasites. Below these 
are given the differences between the concentrations of parasite 
and host, the positive sign indicating higher and the negative 
sign indicating lower osmotic concentration in the tissue fluide 
of the parasite. 
Зада J. Arthur, Gortner, R. A., & Байте 1: у, тһе телен Бе be 
the osmotic concentration of leaf sap and height of leaf insertion in trees 
Sul з ey Club 44: 267—286. 1917. 
er, R. T & Harris, J. Arthur. Notes on the technique of the deter- 
mination of the depression of the бейш point. Plant World 17: 49-53. 1914. 
+ Dixon, Н. H., & Atkins, W. R. С. Osmotic pressures in plants. I. Methods 
of extracting sap from plant organs. Sci. Proc. Roy. ublin Soc. №. S. 13: 422-433. 
1913. Also in Notes from Bot. Sch. 2 Coll. Dublin 2: 154-172. 1913. 
i $ Gortner, R. A., Lawrence, John V., & Harris, J. Arthur The extraction of sap 
from plant tissues by pressure. E Bull. 5: 139-142. М. f. 1916. 
| Harris, i Arthur, & Gortner, R. A. Note on the calculation of the osmotic 
pressure of expressed жағалық saps from the depression of the freezing uu with 
a table for a values of P for А = .001° to А = 2.999°. Ат. Jour. Bot. I: 75-78. 
1014. 
< Harris, J. Arthur. An extension to 5.99? of tables to determine the osmotic 
pressure of expressed vegetable saps from the depression of the freezing point. 
Am. Jour. Bot. 2: 418-419. 1915. 
