276 BOTANICAL GAZETTE .- [SEPTEMBER 
the leaves of the leafy forms. If the same is true of desert Loranthaceae, 
the relationship between leafless and leafy parasite observed by BROWN 
is just the reverse of what might be expected if successful parasitism 
were dependent upon higher osmotic concentration in the tissue fluids 
of the parasite. 
As pointed out elsewhere, however, the technical difficulties in the 
comparison of the tissue fluids of the stems and leaves by the methods 
as yet available for field work are rather great. In the leafless forms 
there is danger of including a considerable amount of fluids from woody 
conducting tissue not at all comparable with that of the green tissue 
which may be taken to be physiologically homologous with the leaf tissue 
of the leaves of the tree or of the leafy Loranthaceae. Furthermore, 
such work as has been done on the rather difficult problem of the physico- 
chemical properties of the tissue fluids of desert Loranthaceae’ is insuffi- 
cient to show that the osmotic concentration is lower in the leafless 
desert forms. Furthermore, the concentration of the sap of desert 
forms seems to vary rather widely, and even if the average concentration 
of the fluids of P. californicum were lower than that of P. macrophyllum, 
it is quite possible that the individual secondary parasite, P. californicum, 
had a higher concentration than its individual P. macrophyllum host. . 
So far as I am aware, the only direct determination of osmotic con- 
centration in primary and secondary parasitism in the Loranthaceae 
is that by Harris and Lawrence (loc. cit.) on the Jamaican broad- 
leaved Phthirusa parvifolia parasitic upon the leafless asoets bese 
gracilis, which is in turn parasitic upon a tree, Cyrilla racemiflora. 
sap properties stand in the following relationship: Cyrilla init 
A=1.18, P=14.2; Dendrophthora gracilis (on Cyrilla racemiflora), 
A=1.26, P=15.2; Phthirusa parvifolia (on Dendrophthora gracilis), 
4=1.49, P=17.9. Osmotic concentration increases from the hos 
the primary parasite and from the primary parasite to the secondary One. 
Note also that the observed secondary parasitism is the leafy P. parvi- 
folia with an average depression of 1.347° upon the leafless D. gracilis 
with an average depression of 1.176°.—J. ArTHUR Harris, Cold S pring 
Harbor, N.Y. 
5 Harris, J. ArtHuR, On the osmotic concentration of the tissue fluids of desert 
Loranthaceae. Mem. Torr. Bot. Club 17:307-315. 1918 
°I have individual determinations on P. californicum which indicate higher con- 
centration than some found in P. macrophyllum. The great difficulty of comparing 
the sap properties of the two forms lies in the fact that, in the neighborhood of Tucson 
at least, they occur in oteg main on different hosts and for the most part in slightly 
different local habita 
