272 Twenty-seventh Annual Report 



growth, and relative resistance to summer and winter temperatures. It 

 was observed in brief that Opuntia castillae and O. ElUsiana made less 

 growth than the other species, but that they were hardier to winter 

 temperatures. With these species growth usually ceased in October 

 while the others often continued growth until severe frosts began in 

 November. Naturally, the tender half-matured joints were killed with 

 the first heavy frost. 



In the summer of 1915, Mr. J. C. Th. Uphof, then assistant in 

 botany in the department of biology, made laboratory studies, morpho- 

 logical and physiological, of joints of these plants in order to determine 

 the factors of cold-resistance in cacti. Mr. Uphof found that the 

 varieties of spineless cacti having relatively thick integuments may 

 v;ithstand a low temperature for a short time with little or no injury 

 while those having thinner integuments would be injured. He also . 

 found that the collecting and freezing of water from the cells in the 

 intercellular spaces during low temperatures is not in itself harmful to 

 the plant. Also, that the protoplasm of the cell is not poisoned with 

 the concentration of the cell-sap solution as a result of at least part of 

 the water of the cell being withdrawn to the intercellular spaces and 

 frozen. Mr. Uphof concluded that with normal cactus plants resistance 

 to cold is inherent in the protoplasm, and for this reason some varieties 

 can endure more frost than others. 



Mr. Uphof's work checked quite closely with observations made 

 by the writer relative to low temperatures in winter. He found that 

 Opuntia castillae and 0. EUisiaiia were more resistant to cold than any 

 of the other species and that Opuntia ElUsiana was considerably hardier 

 than 0. castillae. Mr. Uphof determined that Opuntia castillae would 

 be injured with a temperature of 6.8 degrees F. During the winter of 

 1912-1913, it was severely frozen back on the University grounds with 

 a temperature of 6 degrees F., and in December. 1916, it was injured 

 at the University Farm with an estimated temperature of 9 degrees F. 



The literary work of this bulletin was done by the writer, the 

 reason for this being stated in the publication. 



Timely Hint No. 117, Vines for Shade and Ornamental Planting, 

 was written to meet a growing demand for information on this sub- 

 ject. This leaflet discusses briefly the value of vines for general plant- 

 ing and includes a list of the hardier species, both evergreen and de- 

 ciduous, that are quite generally planted. Short descriptions of the 

 varieties are given together with methods of cultivation. Mnes are 

 among our most ornamental plants. They are planted more in the 

 Southwest than in other parts of the country, partly because of our 



