96 



SCIENCE 



[N. S. Vol. XXXIII. No. 838 



siderably from those reared in a cold room 

 in the mean length of the tail, foot and ear, 

 and the difEerences were transmitted to the 

 next generation. The differences may be 

 reasonably designated as being directly in- 

 dividual and somatic, and as having been 

 transmitted by the germ-plasm, which was 

 not subject to the action of various tem- 

 peratures in the first instance. The reac- 

 tion forms have an additional claim upon 

 ■our attention, since they are the ones which 

 •distinguish northern and southern races 

 of many animals. The crucial test of the 

 value of the alterations induced in the 

 mice is the one applicable to all of the ex- 

 perimentation on this subject, a test in 

 which two parallel series of cultures, one 

 under the altered environment and the 

 other under usual conditions, should be 

 kept going continuously for a longer series 

 of generations, lots being withdrawn from 

 both, from time to time, for continued 

 comparative culture in normal habitat and 

 under other conditions. 



The same considerations apply to Kam- 

 merer's experiments with salamanders in 

 which the reproductive habits of Salaman- 

 dra atra and S. maculosa were altered to 

 resemble each other by specialized ex- 

 posure to climatic factors, and while his 

 later work with Lacerta has resulted in the 

 production of some extremely striking 

 changes in the color bands which behaved 

 in a Mendelian fashion when paired, yet 

 these have not been followed to the third 

 and fourth generations. The permanency 

 of the induced changes seems highly prob- 

 able in this case. There is, however, a great 

 body of properly authenticated evidence 

 which demonstrates conclusively that ex- 

 ternal agencies acting upon bacteria, 

 crustaceans, beetles, fungi and some of the 

 higher types of seed-plants have been seen 

 to result in the appearance of new types or 

 genotypes, which have been found to 



transmit their characters perfectly through 

 so many generations as to indicate prac- 

 tical permanency. 



The names of Beijerinck, Winogradsky, 

 Lepeschkin, Hansen and Barber are asso- 

 ciated with records of mutational occur- 

 rences in pedigreed strains of yeasts and 

 bacteria under pressure of unusual media 

 or other environie conditions. Some aber- 

 rants being propagated by fission and 

 others through the spore stage, some only 

 by selection and others independently. In 

 addition Pringsheim finds many accommo- 

 dative responses to unusual culture media, 

 temperatures and poisons, which may be 

 cumulated and become fixed in these lower 

 organisms, being transmissible by fission 

 or by spores. 



My own earlier work with relation to 

 this subject consisted chiefly of ovarial 

 treatments in which the main and acces- 

 sory reproductive elements of seed-plants 

 were subjected to the direct action of solu- 

 tions of various kinds. A new combination 

 of characters constituting a distinct ele- 

 mentary species or genotype was obtained 

 in one plant, and the divergent type has 

 been found to transmit its qualities in the 

 fullest degree, as far as tested, to the fifth 

 generation. Still more marked forms were 

 obtained in a second genus, the divergent 

 progeny being lost in transference to the 

 Desert Laboratory, while distinct responses 

 have been obtained in the extensions of 

 these experiments upon species represent- 

 ing widely different morphological types 

 in Arizona. The greater majority of the 

 tests have been made upon plants growing 

 under natural conditions, so that environ- 

 mental reaction in addition to that of the 

 specific reagents might be excluded. Prog- 

 enies representing many species, including 

 thousands of individuals, many of which 

 are divergents, are now under observation. 

 Absolute finality of decision with respect 



