VARIATION IN PEDIGREE-CULTURES 225 



test and observation, a matter which may occupy some time, before 

 final announcement. 



Despite general assertions to the contrary, no evidence has yet been 

 obtained to prove that the influence of tillage, ' cultivation,' or the mere 

 pressure of environmental factors has produced any permanent changes 

 in hereditary characters of unified strains of plants. 



The above is not meant as a sweeping assertion that inherited char- 

 acters may not be affected by agents external to the protoplasts that 

 bear them. On the contrary, the experiments now well advanced and 

 conclusively verified, first announced in December, 1905 4 , and here 

 described for the first time, show that saltatory inheritance has been 

 induced by the action of external agents upon the ovules of two species 

 of seed-plants. 5 The alterations in question consist in the total sup- 

 pression of some qualities of the parental form and the substitution 

 therefor of new characters or of a total gain of new qualities in some 

 instances, and the differentiating points between the parental form and 

 the derivative are both anatomical and physiological. 



The atypic form which has been tested to the second generation in 

 one species is found to constitute a mutant in the sense in which that 

 term is used by de Vries, and is a real and actual departure from the 

 course of the hereditary strain. The capacity of the mutants induced 

 in this manner for survival would depend entirely upon the environ- 

 ment into which they might be thrown. 



If we seek a similar possible intervention of external forces which 

 might act upon the plant unaided by man, we might find such influence 

 coming from radio-active substances, such as spring- and rain-water, 

 or from the effects of sulphurous and other gases which are being set 

 free in numberless localities, or the protoplasts most nearly in contact 

 with the egg-apparatus may well excrete substances which would pro- 

 duce the same effect, without regard to the forces which originally 

 caused the disturbances in the extra-ovular tissue. Lastly it is to be 

 said that the actual technique of injection might be imitated in a 

 measure by the action of foreign pollen which might find lodgment 

 on the stigmatic surfaces, and sending down tubes through the style 

 introduce unusual substances to the vicinity of the egg-cell without 

 participating in normal fertilization, which would ensue in the cus- 

 tomary manner. Lastly it is to be said that it would appear that a 

 most prolific source of such disturbances might be expected to result 

 from the stings and lacerations of insects, or the action of parasitic 

 fungi, both sources of the most profound morphogenic alterations in 

 somatic tissues, profusely exemplified by the well-known gall forma- 

 tions of plants. 



4 MacDougal, ' Heredity and Origin of Species.' Reprinted in advance 

 from the Monist for January, 1906. and distributed December 18, 1905. 



The possibility is not excluded that the reagents may have affected the 

 elongating pollen-tubes. 



