DEPARTMENT OF BOTANICAL RESEARCH. 87 



firmed. One of the most interesting results of this investigation is 

 that the cacti, although growing in close association with typical 

 halophytes, have the low osmotic concentration of those growing in 

 non-saline deserts. 



An investigation of the osmotic concentration of the fluids of desert 

 Loranthacese (Mem. Torr. Bot. Club, vol. xvii, p. 307-315,) has demon- 

 strated that the leafless Phoradendron californicum and the leafy 

 P. coryoB and P. macrophyllum of the Arizona deserts show an osmotic 

 concentration which is, roughly speaking, twice as great as that demon- 

 strated by the same methods in the tissue-fluids of the species investi- 

 gated in the montane rain-forest of Jamaica (Harris and LawTence, 

 Amer. Jour. Bot., vol. iii, p. 438-453, 1916). In desert Loranthacese, as 

 in those of the montane rain-forest, the osmotic concentration of the 

 tissue-fluids is generaUy, but not invariably, higher than that of the 

 host. 



A paper on the osmotic concentration of the fluids of epiphytic 

 plants, based on investigation in Jamaica and Florida, is now in press. 

 In this it is shown that the osmotic concentration of the tissue-fluids 

 of epiphytic BromeHaceae, Orchidacese, Piperaceae, and Gesneracese 

 is far lower than that of terrestrial vegetation. In the Jamaican mon- 

 tane rain-forest, where data for direct comparisons for individual habi- 

 tats are available, the epiph^i;es show from 37 to 60 per cent of the 

 concentration characteristic of herbaceous terrestrial vegetation, 

 and from 28 to 44 per cent of the concentration of ligneous terrestrial 

 vegetation. In the Bromeliacese, Orchidaceae, and Peperomia of the 

 Piperaceae the osmotic concentration of the species of the Jamaican 

 montane rain-forest is lower than that of the species of the hummocks 

 of subtropical Florida. 



At some future time it is hoped to deal with the problem of the 

 osmotic concentration of cryptogamic epiphytes and to obtain data 

 on the inorganic and organic constituents of the fluids of epiphytes 

 which will justify further discussion of the physiology of these ecologi- 

 cally remarkable forms. 



PLANT BREEDING. 



Culture of a Potato Hybrid, Solarium fendleri X S. tuberosum {"Salinas"), 



by D. T. MacDougal. 



Cultures of the hybrid between the wild potato of Arizona and the 

 domestic variety cultivated in the vicinity of the Coastal Laboratory 

 have been carried on at the Desert Laboratorj^ at the Coastal Labo- 

 ratory, and on a ranch in the valley of the Carmel River. The coope- 

 rative experiments of Professor George H. Shull, of Princeton Univer- 

 sity, in which an analysis is being made of the domestic parent, have 

 resulted in a separation of a large number of elements of different value. 



