276 KOTAMCAL 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 5 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. macrophylhtm, 

 it is quite possible that the individual secondary parasite, P. californicum, 

 had a higher concentration than its individual P. macrophyllum host. 6 



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. clt.) on the Jamaican broad- 

 leaved Phthirusa parvifolia parasitic upon the leafless Dendrophthora 

 gracilis, which is in turn parasitic upon a tree, Cyrilla racemi flora. The 

 sap properties stand in the following relationship: Cyrilla raccmijlora, 

 A = 1.1 8, P=i4.2; Dendrophthora gracilis (on Cyrilla racemiflora), 

 A = 1.26, P=i5.2; Phthirusa parvifolia (on Dendrophthora gracilis), 

 A =1.49, P=IJ.C). Osmotic concentration increases from the host to 

 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 i .347 upon the leafless D. gracilis 

 with an average depression of i . 176. J. ARTHUR HARRIS. Cold Spring 

 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. 



6 1 have individual determinations on P. californicum which indicate higher con 

 centration than some found in P. macro phyllum. 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 the main on different hosts and for the most part in slightly 

 different local habitats. 



