402 CARNEGIE INSTITUTION OF WASHINGTON. 



lowing winter. Weather conditions for a few days following the trans- 

 planting of seedlings or for a few weeks after seeding have such a pro- 

 found effect upon ecesis that it has proved desirable to repeat these 

 operations at intervals during the spring. 



The clue to ecesis is found in the study of root development, 

 together with determinations of the light intensity in the dense vege- 

 tation of the true prairie. The highest mortality among seedlings 

 nearly always occurs during the first three or four weeks, when the 

 primary root is alone available for absorption and the secondary roots 

 are in process of development. In the case of seedlings developing 

 from seeds sown on the surface, moisture conditions are often favorable 

 in the true prairie, but the light intensity is mostly low. The latter 

 is usually less than 20 per cent at the surface of the soil in dense socie- 

 ties, and it sometimes falls as low as 1 to 2 per cent. Under such condi- 

 tions the seedlings become greatly attentuated and rarely survive 

 the summer. In mixed prairie the reduction in the light is much less, 

 and it is of practically no consequence in the short-grass plains. 



The rapidity with which the root system develops is marked, many 

 transplants reaching the maximum extent during the first season. 

 When they are grown in cultivated soil to eliminate the effect of 

 competition, many sandhill dominants are able to thrive, and not a 

 few species blossom and form seed the first season. The competition 

 of seedlings, transplants, and sods among themselves as well as v/ith 

 the natural cover has been followed closely, especially in such domi- 

 nants as Agropyrum and Bulbilis, which spread rapidly by rootstocks 

 and stolons. The past season has been particularly favorable for 

 growth at Lincoln and Phillipsburg, but so unfavorable at Burlington 

 that even well-established tall-grass dominants have succumbed. 



Climax Formations, by F. E. Clements. 



All of the climax formations and associations of the West have re- 

 ceived some study during the year. This has dealt chiefly with their 

 structure, development, and relationship, but increasing attention 

 is being given to their phylogeny, especially since the Pleistocene. 

 In addition, the developmental system of classification has been fur- 

 ther tested by means of these results, and found to be the only one 

 that takes into account all the criteria and permits the expression 

 of natural relationships. 



The most striking discovery of the year was to the effect that the 

 short-grass plains are not a natural community but an artificial one 

 produced by over-grazing. It has been recognized for several years 

 that much of the short-grass association had been derived from 

 mixed prairie as a result of grazing, but it was not until last year that 

 the evidence began to indicate that this was true of the entire com- 

 munity (Carnegie Inst. Wash. Year Book No. 19: 352). The investi- 



