130 



PLANT SOCIOLOGY 



Table 9. — Osmotic Concentration of Cell Sap (in Atmospheres) at Various 



Seasons of the Year in the Quercus ilex Scrub and in the Brachypodium 



ramosum-Phlomis lychnitis Association 



Quercus ilex and Q. coccifera, on the contrary, give regular curves 

 with feeble maxima in the winter (not visible in the table). To the 

 same group belong Pistacia lentiscus, Phillyrea angustifolia, Smilax 

 aspera, Ruhia peregrina, and Ruscus aculeatus, that is, the vast majority 

 of the woody species of the ultimate climatic association (climax) of 

 the region. 



Annual curves with small minima and maxima appear to indicate 

 that the species in question are in harmony with their environment and 

 do not suffer from lack of water even during dry periods. According 

 to the form of the annual curves, various plants may be designated as 

 belonging to the Viburnum type, the Quercus type, the Cistus type, 

 etc. 



Very high values were obtained for halophytes; e.g., Salicornia 

 macrostachya from a locality near Montpellier gave 44.9 atmospheres 

 on May 18 and 42.0 on June 10. These figures refer to normal plants 

 in their best development. On the same days and growing on the 

 same soil that was somewhat drier, so that these plants were evidently 

 suffering from lack of water, the following results were obtained: 

 Salicornia rnacrostachya, May 18, 82.5 atmospheres; June 10, 79.6 

 atmospheres. 



The dryness thus increased considerably the osmotic values, and 

 the plants which were incapable of increasing their osmotic value were 

 the first to be eliminated. 



On the other hand, plants with milky juice and certain desert 

 succulents do not have, and apparently do not need, high osmotic 

 values. Cereus, Opuntia, Umbilicus, Sempervivum and Sedum agree 

 in exhibiting low sap concentrations often ranging from 5 to 8 atmos- 



