DEPARTMENT OF BOTANICAL RESEARCH. 6l 



work of the summer of 191 1, with the assistance of Mr. J. S. Caldwell, 

 whose results will shortly appear. Attention is now being given mainly to 

 the physics of the subterranean moisture conditions, with the hope that 

 methods may eventually be devised by which these may perhaps come to rest 

 upon a quantitative basis somewhat similar to that upon which our knowl- 

 edge of the aerial water relations is now based. In this new phase of the 

 work Mr. E. M. Harvey has assisted. 



The Water-relations of Sclerophylls and Similar Ecological Types, by 



F. B. Lloyd. 



During the month of July 191 2 the march of transpiration for a series of 

 plant pieces in duplicate was determined in continuation of work begun in 

 191 1. The rates of evaporation were determined simultaneously, and the 

 plant material used will be further studied in order to obtain anatomical 

 facts with which it is desired to correlate the transpiration data. The ex- 

 pression "stomatal surface" will be redefined, and the transpiration rates 

 expressed relative to this. It is hoped in this way to obtain a method of 

 comparing the leaf mechanisms which will give an adequate idea of the com- 

 parative behavior of the various types of sclerophylls. It is evident from 

 the character of the curves expressing the march of transpiration that the 

 behavior of a given species is specific, and different, under the same condi- 

 tions, from that of another species. 



It has also emerged from the determination of the march of transpiration, 

 and pari passu of the rates of growth in Briogonum nudum, that the rate of 

 transpiration and that of growth stand in an inverse relation to each other, 

 growth being checked by incipient "drying," and being stopped altogether 

 when wilting sets in, which indeed frequently causes shrinkage of the tissues 

 to an extent sufficient, it may be, to cause death by drying. 



Physical Relations of Roots to Soil Factors, by W. A. Cannon. 



The field studies on the root-systems of the desert plants which have been 

 carried on by Dr. Cannon have revealed many problems requiring experi- 

 mental treatment by special methods. As an introduction to such studies 

 the general problem of the placing of the root-systems was first selected for 

 attempted solution. To this end it was decided to study the plants growing 

 in soil cultures and to subject them to various conditions, especially concern- 

 ing moisture and aeration. A special form of air-pump was constructed 

 for the study of the air-relation, by which a known amount of air, either 

 constant or variable as desired, can be passed through the soil in use. This 

 apparatus gives at the same time a relative measure of the porosity of 

 the soil used, either as dry or for any percentage of contained moisture. 

 As a check on the results obtained in this fashion, the relative porosity of 

 the soils employed was learned through the use of a mercury manometer by 

 which the height of the water-column, as well as the rate of the ascent of 



