ABSORPTION 161 



States Department of Agriculture for 1905, 267, in Osterhout's "Experi- 

 ments with Plants," and in Detmer, 244. There is a full treatment of the 

 important matter of Adsorption by True and Oglevee in the Botanical 

 Gazette, 39, 1905, 1. A special recording thermometer for soil studies has 

 been invented by MacDougal (Journal of the New York Eotanical Garden, 

 3, 1902, 125). 



The foregoing studies should make clear to the student the 

 physical nature of water absorption, and we approach now the 

 problem of the absorption of minerals. First of all we must 

 make sure of the facts before we attempt their interpretation, 

 and the problem is presented : 



What quantities and kinds of mineral matters occur in common 

 plants? 



Experiment. Select some typical herbaceous plant and, cutting 

 it off close to the ground, quickly weigh it to a decigram. Place it 

 in a suitable dish in the drying-oven until it ceases to lose weight 

 (requiring two or three days), then weigh again, which will give the 

 percentage of water originally present. Then place the dry material 

 in a weighed platinum crucible, fused quartz evaporating dish, or even 

 a piece of hard-glass tubing, and, under a proper hood, gently burn 

 away the organic matter, and determine the weight of the remaining 

 ash. 



Mineral Quantities. A comparison of many tables dealing with the 

 composition of plants has shown that ordinary herbaceous plants approxi- 

 mate conventionally to 90% water, 8% organic matter, and 2% mineral 

 matter. 



The determination of the kinds of the minerals left in the 

 ash involves chemical analysis of the soil, an operation rather 

 impracticable here, though some qualitative determinations 

 can readily be made by methods given by Detmer, 79. But 

 the student should inform himself upon the results of some of 

 the many analyses which have been made, and which are sum- 

 marized in Jost's and Pfeffer's works. In this connection 

 he will find that certain minerals occur constantly, and hence 

 appear to be indispensable, in the higher plants, while others 

 are incidental. This involves the inquiry as to the use or mean- 

 ing to the plant of the indispensable minerals, a subject which 

 is best investigated through water-culture. The methods of 



