GENERAL CONCLUSIONS. 73 



tion. The smaller plant at first lost weight at the rate of 61 grams, while 

 the larger gave but 36 grams. Later the larger plant gave off more 

 water than the smaller. Numerous other comparisons might be formu- 

 lated by reference to the results of weighings, and similar individuality of 

 behavior was found by the long-extended series of measurements. It is 

 evident, therefore, that no equation expressive of relation of vohime, 

 water-balance, and loss in weight may be formulated for the massive cacti 

 described in the present paper. 



The depletion of the water-balance is of course less rapid during the 

 second and succeeding years of exposure of detached plants than during 

 the first year. The data obtained from observations on echinocacti Nos. 

 1, 3, 6, and 7 serve as an example of this fact. The rate during the sec- 

 ond year under equivalent conditions in corresponding seasons is not 

 more than 66 or even 55 per cent of that of the first year. In the absence 

 of any information as to structural changes which might serve as a regu- 

 latory factor, the decrease of the rate may well be attributed primarily to 

 the increased concentration of the sap and its consequent greater osmotic 

 activity. Thus in Carnegiea the proportion of mineral salts in the sap was 

 seen to increase from 1 to 3 per cent, while in Echinocadus an increase from 

 less than 0.8 to 3 per cent of dissolved salts ensued. 



The rate of loss of plants exposed in the open may be as much as 4 to 8 

 times that of plants in inclosed but well- ventilated rooms, in which the 

 direct action of the wind and sun are eliminated. This is apparent even 

 when the plants tested in the shade were much larger than those in the 

 open. 



Observations on a number of specimens show that some gain in weight 

 may be expected in small specimens of Echinocadus detached and kept in 

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

 attributed to hygroscopic absorption. A small plant which had been 

 desiccated for two years, when put in a dark -room- with equable temperature 

 at about 60° F., with the relative humidity 80 to 90 per cent during Feb- 

 ruary and March, 1910, was found to gain 2 grams in six days. 



Carnegiea was seen to lose 63 per cent of its maximum water-balance 

 without disorganization. Echinocadus showed a loss, calculated at about 

 69 per cent of the total balance, without losing the power of growth and 

 repletion of its water-supply. 



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 Echinocadus amount to 2.692 grams per 100 c.c, of which the 

 organic matter is 1.320 and the ash 0.772. The total solids in a desic- 

 cated specimen amounted to 7.060 grams, of which 4.060 was organic and 3 

 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 



