282 HARRIS, GORTNER, AND LAWRENCE: 
The question of differentiation in atmospheric conditions at 
various levels in the forest has long received the attention of 
ecologists. Thus as early as 1888 Schimper* called attention to 
differences in the epiphytic vegetation of the forest floor and 
canopy. Shreve in his studies on Jamaican Hymenophyllaceaef 
and on Jamaican montane rain forest epiphytes in generalf has 
emphasized the same point, referring the observed differences to 
‘‘vertical differences between the climate of the forest floor and 
its canopy.” 
Further light is thrown upon the subject by an examination of 
the specific electrical conductivity of the saps. 
While the values of x measuring the concentration of dis- 
sociated electrolytes do not show as great regularity as do those 
of A measuring the concentration of total solutes, the general 
trend of the relationship between this constant and height of 
insertion is clearly the reverse of that demonstrated by the 
freezing-point lowering. Thus in 46 cases the conductivity de- 
creases§ from lower to higher levels as compared with 29 cases in 
which it increases.|| Thus apparently the saps from higher levels 
are actually less rich in electrolytes than those from the lower 
levels. 
That samples from higher levels are relatively less rich in 
electrolytes is splendidly shown by a comparison of the ratios of 
electrical conductivity to freezing-point lowering, i. e., «/A. These 
are represented in DIAGRAMs 3 and 4. In all but 13 of the 75 cases 
the ratio is lower in the saps from the higher levels. Further- 
* sriincti A ge W. Die epiphytische Vegetation Amerikas. Bot. Mitt. 
a. d. Tropen 1, 
+ Shreve, “i ao on Jamaican Hymenophyllaceae. Bot. Gaz. 51: 184—209- 
IQIi. 
t Shreve, F. A Montane Rain-Forest. Pub. Carn. Inst. Wash. 199: 38-41- 
Igl4. 
§ Botanists who are veer to thinking in physico-chemical terms need 
only remember that specifi trical conductivity is the reciprocal of the resistance 
which is inversely proportional to the concentration of ions of electrolytes. Thus a 
decrease in conductivity indicates a decrease in the concentration of dissociated 
electrolytes. 
|| Confidence in the significance of these differences is increased by the fact that 
the mean value of the negative differences (i. e., those in which the conductivity 
at a lower level is greater than that at a higher level) is oe than that of the 29 
positive differences. 
