Apiul 7, 1005.1 



SCIENCE. 



541 



-might be considered as species by one sys- 

 teiiiatist, and varieties by another, is quite 

 incidental and of very little importance. 

 The main contention lies in the claim that 

 characters of a definite nature appear, and 

 become inactive suddenly, and do not 

 always need thousands of years for their 

 infinitely slow external realization, or for 

 their gradual disappearance from a strain. 



Of course the principal corollary of the 

 mutation-theory is that the saltations in 

 question do result in the production of new 

 species and varieties. As a matter of in- 

 terest it may be stated that the systematists 

 who have seriously examined the adult 

 mutants of the evening-primroses culti- 

 vated in the New York Botanical Garden 

 have unanimously held the opinion that 

 certain ones were to be considered as species 

 and others as varieties. 



Furthermore, these conclusions are con- 

 firmed when the characters of the mutants 

 are subjected to statistical methods of in- 

 vestigation. In the observations of Dr. 

 Shull, which will be presented more fully 

 before the Botanical Society of America, it 

 has been found that qualities of the mu- 

 tants, susceptible of measurement, depart 

 definitely and clearly from the parent-type 

 and fluctuate about a new mean, and do 

 not intergrade with the parental form. 

 The amplitude of fluctuation about the new 

 center 'is greater than that of correspondent 

 parental qualities, and the degree of corre- 

 lation is much less in the mutants than in 

 the parent. This is seen by inspection to 

 be true in one species during the first year 

 of its existence, and is confirmed by the 

 exact observations on other forms a dozen 

 years after their mutative origin. Con- 

 sequently the features in question may not 

 be taken to be in any way the result of 

 selection, but are in themselves new qual- 

 ities. 



Lamarck's evening-primrose offers such 

 striking and easily recognizable examples 



of discontinuous variation, and has been 

 the object of so much detailed study, that 

 we are in danger of giving way to the sup- 

 position that the mutation-theory rests 

 upon the facts obtained from this plant 

 alone. It is to be said, however, that if 

 the evidence obtained from it and all of its 

 derivatives were obliterated, the results of 

 experimental studies which have been made 

 upon mutations in other species, upon the 

 behavior of retrograde and ever-sporting 

 varieties, the occurrence of systematic ata- 

 vism, and of taxonomic anomalies, pelories 

 and other morphological features, would 

 furnish ample support for the conception 

 of unit-characters, and serve to establish 

 the fact that mutations have occurred in 

 a number of species representing diverse 

 groups. 



It is now becoming plainly apparent that 

 the phenomena of hybridization, by the 

 opportunities afforded for the study of the 

 included unit-characters in a segregated 

 condition ; for the analysis of complex char- 

 acters, and of the various principles gov- 

 erning the transmission, activity, domi- 

 nancy, latency and recessivity of charac- 

 ters promises to yield results of the first 

 magnitude concerning the mechanism of 

 descent and heredity. The possibilities, 

 among plants, of crosses between species, 

 comparatively widely different in morpho- 

 logical and physiological constitution, indi- 

 cate that the ultimate generalizations upon 

 hybridism will find a broader exemplifica- 

 tion in plants than in animals. 



It is pertinent to point out in this con- 

 nection that the unguarded use of the terms 

 'variation' and 'mutation' to designate 

 phenomena of segregation and alternative 

 inheritance, when races or species are 

 thrown together in a hybrid strain, is 

 bound to result in much confusion, espe- 

 cially in dealing with plants, since it is well 

 known that direct mutants of either parent 

 occasionally occur in such mixed strains. 



