CISSUS-ECHINOCACTUS. 31 



October 7, 1909. The preparation of Cissits laciniata on a joint of Opuntia 



blakeana, which had been drawn early in the year, east its leaves and a dis- 

 section was made of it. A main root had been formed which penetrated 

 the tissue of the Opuntia for a distance of 2 em., and a few shorter roots 

 had been developed around its base. The dissection was preserved. In 

 this, as well as in all other parasitic arrangements examined, the root- 

 system was not so large as if the parasitic form had been established in the 

 soil, a result noticeable in all incidental and arrang-ed parasitic plants. 



January 8, 1910. All the preparations appeared to have been killed by 

 the low air-temperatures of the previous week (10 F.), which had also 

 destroyed plants of Cissus normally rooted in the soil. 



A second analysis of Opuntia blakeana was made from material freshly 

 cut from a plant on February 8, 1910. The total solids in 100 c.c. of 

 expressed juice were found to amount to 7.65 grams, of which 1.15 grams 

 were ash, showing" an increase in both factors over the proportions present 

 in late summer. The average of 3 determinations of the freezing-point 

 indicated an osmotic pressure of 8.88 atmospheres at a temperature of 

 25 C. The osmotic activity of the sap of this plant therefore seems to be 

 least in the period following the active growth that takes place in the mid- 

 summer rains and increases through the following winter. This increase 

 doubtless continues with the concentration of the sap that ensues as a 

 result of the desiccating effects of the winds and low humidity of the arid 

 foresummer of April, May, and June. 



CISSUS-ECHINOCACTUS. 



Large and well-grown individuals of Echinocactus wislizenii are abun- 

 dant in the immediate vicinity of the Desert Laboratory and a number have 

 been brought in for experimentation upon the accumulation of the water- 

 balance. Some plants in their habitats were used, others were rooted in 

 boxes of sand, and others were held without connection with the soil as 

 indicated. Cavities were made in the ribbed bodies of individuals, some 

 of which weighed as much as 40 kg., on the apical, basal, and median 

 portions of the bodies, both in the ridges and the troughs between. The 

 earlier preparations were sealed with melted gelatine, but this was found 

 unsatisfactory by reason of the changes which take place in this material 

 under the influence of changes of temperature and moisture. Many prep- 

 arations which were successful were not sealed, and plaster was used in the 

 majority of cases. With regard to the slips used as parasites, these 

 were inserted as freshly cut at first, but it was soon found advisable to set 

 them in sand-beds until regeneration had taken place. (Plate 10, B.) 



February 1, 1908. -Several slips were inserted in a large Echinocactus 

 growing in the open. 



April 6, 1908. Some of the preparations were apparently successful, 

 while others were flaccid and drooping. 



April 10, 1908. A number of new preparations with freshly-cut slips 

 were made. 



April 20, 1908. One of the slips in an earlier insertion displayed a 

 developing leaf -bud. 



