Febeuaky 22, 1907] 



SCIENCE 



287 



carefully watched for a year as a host for 

 pearblight. After having practically given 

 this up, however, in March, 1906, I found 

 a striking specimen, badly attacked, at 

 Vaeaville. It had been affected on the 

 blossoms the summer before and several of 

 the twigs contained the living bacilli, they,; 

 having been carried over the winter. It 

 has since been found at Colusa and several 

 other points in California. 



The Causes of Dwarfing in Alpine Plants: 

 Professor Frederic E. Clements, Uni- 

 versity of Nebraska. 

 Much attention has been given during 

 the past eight years to the determination 

 and measurement of the factors that de- 

 termine alpine dwarfing in the Pike 's Peak 

 region of the Rocky Mountains. The work 

 was begun with Bonnier 's conclusions that 

 the factors in dwarfing are stronger light, 

 drier air and lower temperature, as work- 

 ing hypotheses. The behavior of many 

 alpine polydemies which showed dwarf and 

 normal forms at the same altitude, some- 

 times within a few feet of each other, indi- 

 cated that light plays little or no part. 

 Repeated and usually simultaneous meas- 

 urements of light intensity were made in 

 1903, 1904, 1905 and 1906 at 1,900 m., 

 2,600 m. and 3,800 m. Midday readings 

 at the three altitudes gave a value of 1 

 (comparative standard) : in a few eases 

 only, the intensity at 3,800 m. was 1.1 and 

 1.2 It is a well-known fact that the rela- 

 tive humidity increases with the altitude. 

 As a rule, the relative humidity is 5-10 per 

 cent, higher at 3,800 m. than at 2,600 m. 

 and 15-20 per cent, higher than at 1,900 m. 

 The variation is sometimes great, however, 

 both simple and automatic readings giving 

 now and then a lower humidity at the 

 highest altitude. While humidity is not a 

 factor in dwarfing, the reduced air pres- 

 sure leads to increased transpiration, as 

 demonstrated both by batteries of poto- 



meters and by water surfaces. The 

 thermograph records of several years all 

 agree in showing a great and regular de- 

 crease in temperature as the altitude in- 

 creases. The decrease is about 1 1/3° for 

 each 1,000 m., or an average difference of 

 25° F^. between 1,900 m. and 3,800 m. The 

 difference in the length of the season is cor- 

 respondingly marked. The season is four 

 and one half to five months at Manitou 

 (1,900 m.) and two months on Mount Gar- 

 field (3,800 m.). 



Of the factors stated by Bonnier, 

 stronger light and drier air are not true 

 of the region studied, and of course can 

 play no part in dwarfing. Water content 

 is the most important and universal factor, 

 though its action is not at all restricted to 

 alpine regions. Low temperature and 

 shortness of season together stand next in 

 importance, and even the third factor, 

 reduced pressure, has a pronounced in- 

 fluence. 



The Origin of New Forms hy Adaptation: 

 Professor Frederic E. Clements, Uni- 

 versity of Nebraska. 

 For purposes of experimental evolution, 

 a careful census has been kept at Min- 

 nehaha of species that are undergoing 

 modification. This not only gave much in- 

 sight into the methods to be employed in 

 producing new forms experimentally, but, 

 for the region studied at least, it gave de- 

 cisive evidence upon the relative im- 

 portance of the four methods of origin, 

 namely, variation, adaptation, mutation 

 and hybridation. During seven years, but 

 one genus, Machceranthera, showed suffi- 

 cient variation to suggest that new forms 

 might be arising from it in the manner 

 assumed by Darwin. More than one hun- 

 dred species have been recorded and 

 studied in which new forms are arising by 

 adaptation to new or changed habitats. 

 Many of these eeads have been described 



