Febkuaet 28, 1908] 



SCIENCE 



339 



forms of the staminate flowers. For 

 several years this phenomenon has been 

 frequently observed by the vyriter on the 

 Pacific coast. The anthers of the stami- 

 nate flowers in all the eases examined bore 

 mature pollen grains. The pistillate 

 flowers also were normally constituted. It 

 appears, therefore, that the determinants 

 requisite for the production of gametes of 

 each sex are present in the cells of the 

 plant usually spoken of as female. It is 

 possible that we have here a modification 

 in the habit of the plant produced by the 

 conditions of culture. The inherence of 

 the determinants of each sex in a single 

 plant is further shown in the somewhat 

 rare cases in which a plant reproduces by 

 means of runners. In the wild state and 

 under certain conditions of culture the 

 underground runners of the hop plant oc- 

 casionally send up shoots which when ma- 

 ture bear flowers of the opposite sex. 

 The Possible Bole of Light in Relation to 

 Alpine Plants: Professor C. H. Shaw, 

 Medico-Chirurgical College, Philadel- 

 phia. 



Readings with the actinometer and black 

 bulb thermometer in vacuo in the Selkirks 

 seem to prove that, as is commonly be- 

 lieved, light at high altitudes is consider- 

 ably more intense than on adjacent low- 

 lands and that the difference is chiefly in 

 the refrangible end of the spectrum. 



Cultures of plants were made by the 

 writer and Mr. William Moore under ex- 

 perimental conditions. When additional 

 blue-violet light was allowed to fall on 

 plants growing in ordinary daylight, the 

 plants exhibited a distinct structural re- 

 sponse. Leaves were more hairy, and in- 

 ternodes shorter than in the control series. 

 The whole question is therefore open, 

 with the probability that the character of 

 light at high altitudes may have a morpho- 

 genic value differing from that at low 

 altitudes. 



The Causes of Timber Lines on Mountains; 

 Snotu as a Mechanical Agency: Professor 

 C. H. Shaw, Medico-Chirurgical Col- 

 lege, Philadelphia. 



The phenomena of timber line are not 

 adequately explained by the factors which 

 have been assigned. The timber lines of 

 the White Mountains and Adirondacks can 

 well be referred to the drying action of 

 cold winds, but not so those of the Selkirks. 

 In this case snow, acting as a mechanical 

 agency, plays the chief part. It may do so 

 in two ways: 



(a) Small trees are directly broken and 

 abraded by weight of snow or by snow 

 creep. 



(5) Small trees and lower branches 

 which are long held under the late-lying, 

 wet beds of snow, suffer a sort of drown- 

 ing and become a prey to fungi. 



When the struggle of trees for existence 

 is primarily with wind, their height is 

 limited, they grow thickly in level-topped 

 societies, and the upper outposts of the 

 forest are in local depressions or sheltered 

 spots. Wind-cripples have dead or dying 

 tops, often with entire loss of the conical 

 shape; the growth of their branches is 

 limited to a critical line. This leads to a 

 densely branched and often one-sided 

 habit. 



On the other hand, when the struggle of 

 trees for existence is primarily with snow, 

 the forest as altitude increases is resolved 

 into groups of trees. These become more 

 separated, and the upper groups of the 

 trees occupy ridges and local elevations. 

 Snow-cripples possess the spire form, with 

 flourishing upper shoots, but the lower 

 branches and foliage are dying or dead, 

 broken by snow and attacked by fungi. 



The alpine fields of the Selkirks, which 

 begin at about 6,000 feet, are thus chiefly 

 due to snow. Higher up the characteristic 

 forms of wind-cripples are seen. 



