84 



SCIENCE 



[N. S. Vol. XL. No. 1020 



hundred of its seedlings. The differences 

 are easily seen even in young plants and 

 iare mostly large enough to constitute new 

 races. The more common ones of these 

 races are produced repeatedly, from the 

 seed from the wild plants as well as in the 

 pure lines of my cultures. It is obviously 

 a constant and inheritable condition which 

 is the cause of these numerous and repeated 

 jumps. 



These jumps at once constitute constant 

 and ordinarily uniform races, which differ 

 from the original type either by regressive 

 characters or in a progressive way. By 

 means of isolation and artificial fecundation 

 these races are easily kept pure during 

 their succeeding generations. 



I shall not insist here upon their special 

 characters. The most frequent form is 

 that of the dwarfs, CEnothera nanella, and 

 the rarest is the giant, or 0. gigas, which 

 has a double number of chromosomes in its 

 nuclei (28 instead of 14) and by this mark 

 and its behavior in crossing proves to be 

 a progressive mutation. Other new types 

 which are produced yearly are 0. rubri- 

 nervis, 0. oblonga and 0. albida. 0. lata 

 is a female form, producing only sterile 

 pollen in its anthers and 0. scintillans is in 

 a splitting condition, returning every year 

 in a greater or less number of individuals 

 to the original type from which it started. 

 Besides these there are a large number of 

 mutations of minor importance, many of 

 which have not even been described up to 

 the present time. 



Thus we see that the experiments pro- 

 vide us with a direct proof for the theory 

 of evolution. They constitute an essential 

 support of the views of Darwin, and more- 

 over they relieve them of the many objec- 

 tions we have quoted and bring them into 

 harmony with the results of the other 

 natural sciences. 



But, besides this, they show us the way 



into a vast new domain of investigation and 

 afford the material for a study of the in- 

 ternal and external causes which determine 

 the production of new species, at least in 

 those eases in which, as in the primroses, 

 mutations are relatively abundant. From 

 these we may confidently hope to come 

 some day to the study of those rarer muta- 

 tions on which the differentiation of the 

 main lines of organic evolution seem to 

 have depended. Hugo de Veies 



University op Amsterdam 



TSE PBOBLEM OF LIGSTING IN ITS RE- 

 LATION TO TEE EFFICIENCY OF 

 TEE EYE1- 



Up to the present time the work on the prob- 

 lem of lighting has been confined almost en- 

 tirely to the source of light. The goal of the 

 lighting engineer has been to get the maxi- 

 mum output of light for a given expenditure 

 of energy. Until recent years little attention 

 has been given to the problem in its relation 

 to the eye. It is the purpose of this paper to 

 outline in a general way some of the more im- 

 portant features of this phase of the subject, 

 and to give some of the results of work that ia 

 now being done on the problems that these 

 features present. 



Confronting the problem of the effect of 

 lighting systems on the eye, it is obvious that 

 the first step towards systematic work is to 

 obtain some means of making a definite esti- 

 mate of this effect. The prominent effects of 

 bad lighting systems are loss of efficiency, 

 temporary and progressive, and eye discom- 

 fort. Three classes of effect may, however, 

 be investigated: (1) the effect on the general 

 level or scale of efficiency for the fresh eye; 

 (2) loss of efficiency as the result of a period 

 of work; and (3) the tendency to produce dis- 

 comfort. Of these three classes of effect the 

 last two are obviously the more important, 

 for the best lighting system is not the one 

 that gives us the maximum acuity of vision 



1 This paper, with, some changes, was read be- 

 fore the American Philosophical Society of Phila- 

 delphia, April 4, 1913. 



