Febeuart 28, 1908] 



SCIENCE 



337 



two corresponding elementary forms of B. 

 bursa-pastoris, and appearing just as in 

 that ease in the ratio, 9AB : 3aB : 3Ab : lab. ■ 

 This ratio appeared in combination with 

 each type of capsule, so that B. Eeegeri 

 now exists with four types of rosette. 



The form of capsule is a perfectly alter- 

 native character, but the i^, hybrids have 

 the Heegeri type of capsule in only one in 

 18 to 25 individuals. 



The fact that B. Heegeri has the same 

 Mendelian units in its leaves as are pos- 

 sessed by B. bursa-pastoris is held to 

 further confirm its direct derivation from 

 that species. 



By hybridization many elementary 

 forms are produced from a small number 

 of initial mutations, and the whole series 

 of such elementary forms occurring in one 

 species may be paralleled in a nearly re- 

 lated species by the same means. 



The smallness of the ratio of occurrence 

 of the Heegeri type of capsule indicates 

 that that species owes its capacity for self- 

 maintenance in competition with its parent, 

 to the comparative infrequeney of cross- 

 fertilization. 



The Effect of Heat on the Starch Grain: 

 Professor H. Keaemer, Philadelphia 

 College of Pharmacy. (By title.) 



The Relation of Plant Societies to Evapo- 

 ration: Professor E. N. Transeau, East- 

 ern Illinois State Normal School. 



Methods for the Control and Measurement 

 of Soil Moisture: Dr. Burton E. Liv- 

 ingston, Carnegie Institution of Wash- 

 ington. 



For controlling soil moisture, a porous 

 cup (of the form used in the evaporation 

 studies described in Publication No. 50 of 

 the Carnegie Institution and in the Plant 

 World for December, 1907) is connected 

 by rubber stopper and glass, rubber or lead 

 tubing to a reservoir of water, and the cup 



is buried in the soil of the pot or other 

 culture container. After equilibrium has 

 been attained, water is taken into the soil 

 only as fast as it is removed. The height 

 of the reservoir, and hence the length of 

 water column to be lifted, determines the 

 amount of moisture which will be main- 

 tained in the soil. The reservoir may be 

 of any size, so that the culture may be con- 

 tinued for an indefinite period without 

 attention. The device for measuring soil 

 moisture is essentially the same apparatus 

 as that just described, so arranged that 

 the cup may be filled and emptied at will 

 by means of two tubes which extend above 

 the soil surface. The rate of water flow 

 into the soil, taken for a short period 

 beginning with the filling of the cup, is an 

 index to the attraction of the soil for 

 moisture, and therefore to its moisture 

 condition, the instrument having been 

 previously calibrated for the particular 

 soil question'. 



Some Unsolved Problems of the Prairies: 

 H. A. Gleason, University of Illinois. 

 Rapid settlement has almost completely 

 destroyed the prairies of the eastern arm 

 of the prairie province, leaving a number 

 of important ecological questions unsolved. 

 Among them are: (1) The original causes 

 which led to the occupation of the terri- 

 tory by forest rather than by praii'ie; (2) 

 the order of invasion of the prairie flora; 

 (3) the manner and rate of invasion of the 

 forests from the southeast; (4) the rela- 

 tion of prairie fires to the forest; (5) the 

 tension lines between the upper austral 

 prairies and the transition forest on the 

 north and the lower austral forest at the 

 south; (6) the structure and composition 

 of the prairie associations. Some of these 

 can never be solved completely, but care- 

 ful studies on the scattered fragments of 

 prairies still available may even yet do 



