348 CARNEGIE INSTITUTION OF WASHINGTON. 



Statistical Studies, hy H. M. Hall. 



A beginning has been made in the apphcation of statistical methods 

 to the solution of problems in the taxonomy of the higher plants. 

 In some cases this can best be carried out in the field. Thus, the num- 

 ber of ray-flowers, disk-flowers, and involucral bracts has been deter- 

 mined for 167 heads at two field stations, and these observations are 

 being extended to other species in order to test the constancy with 

 which the number follows some system. Laboratory studies have 

 dealt with the variation in the number of ray-flowers and disk-flowers in 

 several species of Artemisia at different stations, as well as the degree 

 of fluctuation at a single station and for an individual plant. Some- 

 what different is the case of a polymorphous species of Chrysothamnus, 

 of which 150 specimens from as many localities were subjected to an 

 examination involving about 1,200 measurements. By this means the 

 variation in the ratio of length of style or appendage to the length of 

 the style-branch and also the ratio between the length of the lobe and 

 the tube of the corolla have been established. Similar studies have 

 been made in a number of other species. The results thus far obtained 

 have been used in determining the degree of constancy of systematic 

 characters and in furnishing evidence of value in ascertaining the 

 relationships of certain forms. It is hoped to extend quantitative 

 methods to all the genera to be monographed, as well as to the experi- 

 mental study of criteria. 



Adaptation and Mutation as a Result of Fire, hy F. E. Clements. 



As a consequence of fire at the Alpine Laboratory in 1917, the herba- 

 ceous layer of the Douglas-fir forest was exposed to the sunlight. 

 This led to the modification of the subdominants into sun-forms, 

 closely approaching adjacent forms commonly regarded as species in 

 some cases and in others producing a new and characteristic sun-form. 

 Chief among the former were Mertensia pratensis, modified into a form 

 approaching M. lanceolata, and Erigeron glahellus, changed to resemble 

 closely E. macranthus. In neither case does this amount to identity, 

 but the modification progresses each year under influence of sunlight. 

 Statistical studies have been made of the present stage of adaptation 

 and will be repeated each year as long as the process continues. 



The most striking consequence of the fire was the apparent origin 

 by mutation of a new form-genus of grasses. A normal though 

 luxuriant bunch of Elymus, which had been under observation earlier, 

 developed 3 to 4 spikelets with long pedicels at each joint, instead of 

 1 to 2 sessile spikelets. The pedicels were 10 to 15 mm. long in 1918 

 and widely spreading, giving the appearance of a narrow panicle. In 

 1920 the lateral spikelets had become short-stalked, while the two 

 central still had long stalks. The spikelets were slender and terete 



