CORRELATION OF DISTRIBUTIONAL FEATURES. 577 



corresponds to the northeastern portion of the humid province, as 

 shown on the latter chart. The northwestern areas of medium and 

 high product values correspond, to a degree, with the similar semihumid 

 and humid provinces on the moisture chart. 



The eastern half of the product chart resembles a temperature 

 chart in its zonation, as has been mentioned, and shows no clear rela- 

 tion to the moisture-ratio chart, excepting that the southeastern area 

 of very high moisture-temperature values may be considered as corre- 

 sponding to the southeastern humid area in the latter case. Only this 

 eastern half needs, therefore, to be specially compared with the vegeta- 

 tion charts, and in this comparison the southeastern area (of very 

 high products and of high moisture ratios) may be left out of account. 

 The comparison brings out the fact that there are but two cases where 

 any striking agreement in form and position of areas is to be detected. 

 Quercus alba (plate 18) occupies, roughly, the provinces of medium, 

 high, and very high product values, but this species does not extend 

 nearly as far westward in the southwestern part of its area as does the 

 province of medium moisture- temperature products. Also, this tree 

 does not occupy peninsular Florida, which includes the highest product 

 values. Quercus alba may be said mainly to correspond, in its dis- 

 tributional area, with the region having moisture-temperature indices 

 ranging from 4 to 22, but in the southwestern portion of its area it 

 extends westward only about as far as index- value 17. This is pot to 

 be considered a very satisfactory agreement. 



The other case where an apparent agreement between moisture- 

 temperature product zones and vegetation areas is to be detected is 

 that of the cumulative distribution of southeastern deciduous trees 

 (plate 4). In this case the agreement is more nearly perfect than for 

 Quercus alba, but here, also, the vegetation area does not extend south 

 in Florida far enough to include the very highest product value. These 

 15 trees, considered together, occupy the provinces of high and very 

 high product indices, except the very highest, and with the further 

 exception that they extend much farther westward in Texas than does 

 the province of high index values. These trees may be considered as 

 occupying the region having moisture-temperature indices ranging 

 from 7 to 23, but they extend to index-value 2 in Texas. 



On the whole, we are once more led to the conclusion that the mois- 

 ture-temperature products do not furnish a criterion of great general 

 value, as far as the discovery of distributional correlations is concerned, 

 at least for the vegetation areas that we have charted. Of course, many 

 areal correlations not here mentioned are to be found between our 

 vegetation charts and the chart here considered, but most of these 

 represent cases where this chart agrees, in its zonation, with the mois- 

 ture charts, and a number of such correlations have been noted in 

 connection with those. 



