94 MASS. EXPERIMENT STATION BULLETIN 210. 



The peach (Fig. 5) quite closely follows the plum in its resistance to 

 calcium arsenate, and the two figures (4 and 5) show no more difference 

 than might perhaps easily disappear could a greater number of tests have 

 been made. 



The elm (Fig. 6) is evidently less resistant to pure acid calcium arsenate 

 than the pear, as eleven cases of injurj^ were obtained above the safety 

 line AB of the figure, in clear-weather tests, and the line itself runs con- 

 siderably lower than that for the pear. In cloudy weather the elm also 

 appears to be more easily injured at high humidities, even if the tempera- 

 ture is low. 



Commercial Calcium Arsenate with 1 Per Cent Milk of Lime. — On the 

 apple (Fig. 7) this material gives results differing little from those ob- 

 tained with the pure acid calcium arsenate described above. The cloudy 

 weather tests suggest a little greater safety with the commercial mate- 

 rial at medium combinations of temperature and humiditj'', but the rather 

 small number of tests obtained makes this difference less significant than 

 if similar results had been shown by a larger number. 



In the case of the pear (Fig. 8) no injury was obtained following any 

 of the tests, and AB is simply placed along the highest tests obtained. 

 Whether higher combinations of temperature and humidity would have 

 shown injury could thej'- have been obtained, is, of course, unknown. 

 The cloudy weather safety line CD is more satisfactorily located, three 

 cases of injury having shown that the line could not be placed higher. 



Tests of the cherry (Fig. 9) give in general an agreement between the 

 two materials (compare Figs. 3 and 9), though the commercial substances 

 seem, as in the case of the apple, to be a little safer at medium combina- 

 tions of temperature and humidity. 



With the plum (Fig. 10) it would seem that the commercial material 

 can be used with safety at a considerably higher temperature than the 

 pure when the humidity is low (86° as compared with 79° at 50° humidity) . 

 Aside from this, nothing of significance appears on comparing Figs. 4 

 and 10. 



On the peach (Fig. 11) the two materials give almost identical results 

 (compare Figs. 5 and* 11). On the elm (Fig. 12) the commercial article 

 appears to be safer in clear weather than the pure substance (compare 

 Figs. 6 and 12), although one doubtful injury at 85° humidity suggests 

 that the point B on Fig. 12 may be too high. 



Comparison of the safetj'' lines obtained on the different kinds of foliage 

 tested with commercial calcium arsenate in clear weather brings out sev- 

 eral points of interest. The elm (Fig. 13, 2) would at first seem to be more 

 resistant than the pear (1), particularly at high T and low H. It should 

 be remembered, however, that line 1 was located along the highest tests 

 obtained, no injury showing up to that line, and no tests being available 

 above it. It is not improbable that this line could go considerably higher 

 than where it is now located. The cherry (4) is more resistant than the 

 plum (5) at high T, but slightly the reverse holds at high H, and both, 



