DEPARTMENT OF BOTANICAL RESEARCH. 6l 



well-ventilated rooms during January and December. This gain may be at- 

 tributed to hygroscopic absorption of the dead spines. A small plant which 

 had been desiccated for two years, when put in a dark room with equable 

 temperature at about 6o° F., with the relative humidity 80 to 90 per cent 

 during February 1910, gained 2 grams in 10 days, and the same plant also 

 increased its weight 4 grams in 24 days in 1909, during the first year of its 

 desiccation. It is to be pointed out that the water taken up in this manner 

 could be of no practical use to the plant, since the fluid would be held so 

 tenaciously by the tissues of the dead spines that it could not be withdrawn 

 by the osmotic activity of the living cells. 



An inspection of the proportions of organic material and ash shows no 

 relative variation in the sap of plants in which the supply of water had been 

 partially depleted by desiccation. The total solids in the juice of a turgid 

 Bchino cactus amount to 2.692 grams per 100 c.c, of which the organic mat- 

 ter is 1.320 and the ash 0.772. The total solids in a desiccated specimen 

 amounted to 7.060, of which 4.060 were organic and 3.0 ash. The general 

 concentration had been increased in the ratio of 2 to 7, the concentration of 

 organic matter from 1.3 to 4, and the concentration of the ash as 1 to 3. The 

 total solids dissolved in the sap of a turgid Carnegiea amounts to 3.4 parts in 

 a hundred, of which 2.4 are organic material and 1 ash. In the desiccated 

 plant the dissolved solids amount to 9.6 parts in 100, of which 6.8 are organic 

 and 2.8 ash. The general concentration was as 3.4 to 9.6, the concentration 

 of organic material as 2.4 to 6.8, and of the ash as 1 to 2.8. 



An examination of the chemistry of these forms might probably lead to 

 results of value in the interpretation of their development. The cacti of the 

 Tucson region, and probably all of these forms, are rich in calcium carried 

 in solution in the sap as an accident of its occurrence in abundance in the 

 soil. The sap shows a high degree of osmotic activity, ranging from 5 to 12 

 atmospheres in various species in a state of maximum turgidity, to perhaps 

 twice this pressure when the water-balance is depleted. Furthermore, these 

 plants, especially the halophytes, are known to be capable of an accommoda- 

 tive reaction, by which the osmotic pressure may be automatically increased 

 in response to the increased concentration of the soil solutions. (See Publi- 

 cation No. 141.) 



The Root-habits of Desert Plants (by Dr. W. A. Cannon) : 



A general resume of the investigations upon the root-habits of plants in 

 the vicinity of the Desert Laboratory has been made in Publication No. 131, 

 and Dr. Cannon is now carrying on observations of similar purpose and 

 scope upon the vegetation of Algeria and along the Nile in Egypt. Of the 

 many important generalizations now sustained by results at hand, a few of 

 the more obvious are as follows : 



The root-systems of the rapidly-growing summer annuals of the desert 

 are different from those of winter annuals, in showing a fuller development 



