OSMOTIC PRESSURE OF TISSUE FLUIDS 
447 
each. They cannot therefore be considered important, but are in- 
cluded for the sake of completeness merely. It is interesting to note 
that numerically they are smaller than the positive differences. 
With numbers so small as those involved in the series of deter- 
minations for the individual species, it is idle to calculate probable 
errors. This has, however, been done for the whole series.^^ 
The results are: 
For parasites A = 1.282 ± .018, P = 14.43 
For hosts :A = 1.129 ± .026, P = 13.59 
+ 0.153 d= .032 + 1.84 
The difference is over four and one half times as large as its probable 
error. 
In the diagrams and the averages we have included every pair of 
determinations available for the Jamaican series to avoid any possible 
criticism concerning the selection of data. Some of the cases in which 
the leaves of the host are recorded as exhibiting a higher osmotic 
pressure than those of the parasite are perhaps capable of explanation. 
Consider these cases in detail. 
The exceptions to the rule of the higher osmotic pressure of the 
sap of the parasite are the following: 
203 . Phthirusa parvifolia A = 1.181 
on Vaccinium meridionals A = 1.252 
0.071 
247. Dendrophthora cupressoides A = 1.258 
on Baccharis scoparia A = 1.276 
0.018 
447. Dendrophthora gracilis A =1.19 
on Vaccinium meridionale A = 1.355 
0.164 
508. Phthirusa pauciflora A = 1-593 
on Citharexylum caudatum A = 2.027 
0.434 
509. Dendrophthora opuntioides A = 1.165 
on Oreopanax capitatum A = 1.525 
0.360 
^2 Statistically the process of combination of diverse species of parasites and of 
the various species of hosts seems quite legitimate, since the heterogeneity will tend 
to increase the magnitude of the calculated probable error. 
