November 24, 1916] 



SCIENCE 



'61 



Thais feeds in this region on barnacles and mus- 

 sels. It is destroyed (1) by eannabalisni within 

 the egg capsule; (2) by fish when young; (3) by 

 herring gulls when old; (4) by shore ice in the 

 winter. A comparison of collections made on is- 

 lands on which the gulls breed, with situations 

 where there are not so many, seems to show that 

 the proportions of color found are determined by 

 selection. 



An Inquiry into the Relative Importance of the 

 Various Phases of the Environment in Deter- 

 mining Plant Distribution: Wm. E. Lawkence. 

 This paper presents the results of an inquiry 

 into the literature to ascertain what researches 

 throw light on the problems of plant distribution. 

 It includes a discussion of the relative importance 

 of phylogeny, historic geology, climatic cycles, 

 topography, climatic and edaphie factors as they 

 affect the distribution of plants. The inherited 

 physiological and morphological characteristics of 

 a plant, on account of its phylogenetie relation, 

 are considered first because they define the limit 

 of the plant 's response in terms of the environ- 

 ment. Geological factors have, of course, greatly 

 influenced the preceding, but they are equally im- 

 portant in determining the components of the 

 endemic flora. Climatic and edaphie factors are 

 effective at present. Of these no one factor or 

 combination of factors is found to be all domi- 

 nant. Under certain less variable conditions or 

 combination of factors, the more variable factor 

 or factors appear to dominate the physiological 

 activity of the plant and hence determine its suc- 

 cess in such an environment. There are, therefore, 

 no limiting factors in plant distribution except as 

 the conditions are defined. Under proper condi- 

 tions every known factor in nature may limit 

 growth and reproduction, hence distribution. The 

 control of these conditions one by one is exactly 

 the method of experimentation. "When we at- 

 tempt to analyze the natural conditions, we merely 

 interpret according to the laws of experimenta- 

 tion. There seems to be good reason to believe 

 that the distribution of certain plants and plant 

 associations are in some cases limited by one fac- 

 tor such as water and in other cases by other fac- 

 tors such as temperature. The whole situation is 

 likely to be obscured in nature because of the in- 

 numerable possibility of combination and the fac- 

 tors of preoccupation and competition. An ecolog- 

 ical classification is presented based upon the 

 greatest variable factor for any given area, 

 whether the area is denned on the basis of physi- 

 ography, plant association, or other limits. 



On the Relation between the Rate of Root Growth 



and Oxygen: W. A. Cannon. 



A series of experiments is reported on in which 

 the roots of Prosopis velutina and of Opuntia 

 versicolor are exposed to atmospheres of (1) pure 

 carbon dioxide, (2) and atmospheric air so di- 

 luted with carbon dioxide that a mixture contain- 

 ing 5 to 25 per cent, oxygen results. It was found 

 that the roots of both Prosopis and Opuntia can 

 maintain a feeble growth rate in an atmosphere con- 

 taining as little as 5 per cent, oxygen, but that 

 root growth in both species stops in pure C0 2 . The 

 recovery from the asphyxiation occurs sooner in 

 Prosopis than in Opuntia, and in both at higher 

 sooner than at lower soil temperatures. The re- 

 sults indicate that the response of the roots of 

 Opuntia to a diminished oxygen supply, such as 

 occurs with increasing depth beneath the surface 

 of the ground, is a contributory factor among 

 those which bring about the superficial placing of 

 its roots. 



The Relation between Marine Biology and Ecol- 

 ogy: Ellis L. Michael. 



To understand marine organisms is the func- 

 tion of marine biology. To what extent, how, 

 and why are marine organisms adapted to the 

 particular environments in which they live? In 

 short, by virtue of what is a marine organism 

 marine? This is the central question in marine 

 biology: all others are strictly tributary to it. 

 Fully grasped, this means that the significance of 

 no phenomenon essential to the life of any marine 

 organism can be fully understood so long as any 

 other phenomenon likewise essential to it is en- 

 tirely ignored. Knowledge of the environment is 

 therefore as indispensable to a complete under- 

 standing of marine organisms as is that of the 

 organisms themselves. Continuous and intimately 

 coordinated investigations in chemistry, physics 

 and hydrography as well as in morphology, em- 

 bryology and physiology are indispensable. There 

 is, therefore, a certain natural order of progress in 

 marine biology. Details can not be stipulated, 

 but this much is certain: after the various organ- 

 isms to be investigated have been identified, it is 

 necessary to determine how they are related to the 

 elements of their environmental complexes before 

 it will be possible to discover how or why these 

 relations are maintained. That is, the initial step 

 must be one in field ecology. Then would follow 

 the more intensive studies of structure, function 

 and behavior — morphology, embryology, physiol- 

 ogy and experimental ecology — required to fully 



