CISSUS-ECHINOCACTUS. 33 



The variations in the- sap are emphasized by comparison with the results 

 obtained from the analysis of a small specimen in a turgid condition, 

 from the bajada west of the Desert Laboratory, on vSeptember 9, 1909. 

 The acidity was found t< i be equivalent to 0.0887 gram of H,S0 4 per 100 c.c. 

 The total solids amounted to 2.092 grams, of which 0.772 gram was inor- 

 ganic or ash. The total solids dissolved were thus seen to vary from 2 to 

 7 per cent and the inorganic constituents from less than 0.8 per cent to 3 

 per cent. 



Dr. B. E. Livingston determined the osmotic condition of the sap of 

 Echinocactus (Carnegie Institution of Washington Pub. No. 50, p. 70, 1906) 

 at a season not mentioned in the original publication, but suggested by 

 him to be in August, while still turgid from the summer rains, in which the 

 osmotic pressure was found to average 3.94 atmospheres by the freezing- 

 point method and 3.6 atmospheres by the boiling-point test. 



An analysis of the sap of a plant taken from the slopes near the Desert 

 Laboratory, February 5, 1910, gave total solids of 3.18 grams per 100 c.c. 

 of sap, of which 1.20 grams were inorganic or ash. The average of 3 

 freezing-point tests indicated an osmotic activity of 5.72 atmospheres at 

 25 C, which would be a normal increase in the concentration over that 

 by Livingston, noted above. Like other cacti, the concentration would 

 doubtless increase until the beginning of the summer rains. The inor- 

 ganic solids obtained by our analysis of September, 1909, amounting to 0.772 

 gram per 100 c.c, would indicate a freezing-point of 3.67 atmospheres on 

 the assumption of practical uniformity of composition of sap. The total 

 solids in the sap of Echinocactus taken in June, 1910, had risen to 6.75 per 

 cent, of which 2 per cent was ash, while the freezing-point tests indicated 

 an osmotic pressure of 10 atmospheres. Stems of Cissus at this time 

 yielded a sap containing 7.88 per cent solid material, of which 2.24 per 

 cent was ash. The average osmotic pressure was equivalent to 11.3 

 atmospheres, not much higher than that of the enforced host. 



November V, 1909. A dissection of another arrangement showed that 

 the base of the inserted slip had died, but a root arising from the free sur- 

 face had extended down into the wound-cavity of the host, where it branched, 

 the branches either adhering closely to or penetrating the tissues. Four 

 undisturbed arrangements now remained, the other three having perished. 



January S\ 1910. A few preparations in the laboratory were still alive, 

 but in a quiescent condition. The inserted slips were lax and slightly 

 shriveled. It seems clear from the evidence offered by all of the exper- 

 iments that the amount of liquid which may pass through the base of an 

 inserted slip of Cissus from Echinocactus is not sufficient to supply a larg'e 

 shoot, although the balance of pressure on the side of Cissus is very great 

 at times. 



