OSMOTIC PRESSURE OF TISSUE FLUIDS 
439 
We have therefore determined by means of the cryoscopic method 
the osmotic pressure of the tissue fluids of host and parasite. 
II. Materials and Methods 
In the late winter and early vSpring months of 191 5, we had the 
opportunity of spending some weeks in a study of the concentration of 
the saps of the plants of the Coastal Deserts and of the Montane Rain 
Forest of the Blue Mountains of Jamaica, splendidly described and 
illustrated by Shreve (1914). In the latter habitat Loranthaceae are 
abundant. York (1913) has given a detailed account of the mor- 
phology of two of the seven species which we have studied. 
The parasites, structurally and physiologically considered, fall 
into two groups, those with and those without leaves. 
The leaves of Phthirusa and Phorodendron may be looked upon as 
comparable with those of the host. Such can not legitimately be 
assumed of the green stems of the three (physiologically) leafless 
Dendrophthora species. In all the determinations based on these 
species, we had some difficulty in deciding what parts of the tissue of 
the parasite to include. It would obviously be quite illegitimate to 
compare the most tender recent growth of the parasite with the 
matured leaves of the host. It would also be quite wrong to draw 
the comparison between juices pressed from the oldest stems of the 
parasite with the leaves of the host tree. Possibly the best method 
would have been to scrape the green tissue from the outside of the 
parasite stems, but this would have entailed a very great deal of time 
and would have exposed the constants to obvious criticisms. Further- 
more this method while applicable to Dendrophthora gracilis and D. 
opuntioides could not well be used for D. cupressoides. We decided, 
therefore, to include the whole of the obviously mature axis tissue, 
omitting only the very young growth, when such was present, and the 
older heavier stems which while once physiologically leaf homologs 
could not possibly be still so considered. 
The technique used was very simple. Samples of the tissue of the 
parasite and host were collected in test tubes of about 100 cc. capacity 
and taken to the laboratory for freezing by immersion for several 
hours in an ice and salt mixture. The sap was then extracted by 
pressure in a small heavily tinned press bowl with a powerful hand 
screw. After filtering, the freezing point lowering of the sap was 
determined by the use of a thermometer graduated in hundreths of 
