126 



SCIENCE 



:N. S. Vol. XXVII. No. 682 



ties borne by mature plants produced. 

 The modifications, of whatever character 

 they may be, are probably beyond observa- 

 tion by cytological methods. 



In addition to these direct effects it is 

 within the range of possibility that the 

 application of the reagents might set in 

 motion the processes resulting in poly- 

 embryony, or parthenogenesis: it is to be 

 noted, however, that the facts at hand do 

 not suggest such a happening in the forms 

 already obtained, but in the extension of 

 these experiments to various types of re- 

 production these things must be taken into 

 account. 



While the method described is of interest 

 as having possibilities for our interven- 

 tion in the evolution of organisms, it be- 

 comes much more so if similar results may 

 be expected in a state of nature. 



Such a parallelism is to be found in the 

 unusual intensities of the environic factors 

 of light, temperature, moisture, etc., which 

 have been used by Tower in the modifica- 

 tions of Leptinatarsce which he has secured. 

 Here, of cotirse, the entire soma as well as 

 the germ-plasm is subjected to the action of 

 the inciting agent. The various distribu- 

 tional agencies by which seeds are con- 

 stantly being carried far beyond the limits 

 of the customary range of their various 

 environmental conditions must result in 

 the exposure of developing individuals and 

 mature germ-plasm to unusual intensities 

 which might well be responsible for such 

 resu],ts. Thus, a stream takes its rise near 

 the alpine plantation of the Desert Labora- 

 tory, and flows out on the desert a few 

 miles away, and a mile lower down. 

 Doiibtless hundreds of thousands of seeds 

 are carried to the lowlands feach year. 

 Some of these develop into individuals 

 which carry out reproduction. This is 

 usually done in the native habitat, at 

 actual temperatures of the tissues not 

 above 60° or 70° F. Down below, spore 



formation, reduction divisions and ferti- 

 lization may ensue in temperatures 40° 

 to 50° higher, a difference capable 

 of being endured by the shoots of 

 some plants, now being tested, and 

 which might well cause irreversible de- 

 velopmental changes. Other factors of 

 the environment may operate in a similar 

 manner. Again, it is to be recalled that 

 the actual formation, or intrusion of active 

 substances in the ovarial tissues, may result 

 from the stings of insects, the mycelia of 

 parasitic fungi, the penetration by foreign 

 pollen, or the egg or pollen may become 

 subject to radium emanations or to X-rays 

 or other forms of radiant energy. Still 

 another possible action is to be accounted 

 for: in hybridization the foreign pollen 

 tubes, carrying the generative nuclei of 

 the pollen parent, may encounter sub- 

 stances in the invaded pistil to which they 

 are not usually subject, with the result that 

 their capacity for transmission of parental 

 characters may be altered, and qualities 

 may thus appear in the progeny which are 

 not active in either parent. 



A hypothetical consideration of the 

 known facts as presented by the many 

 species in which mutation has been seen to 

 occur seems to lead to the conclusion that 

 the changes upon which discontinuity of 

 inheritance rests, ensue previous to the re- 

 duction divisions in plants. The altera- 

 tions which take place in my experiments 

 however, follow disturbances not brought 

 to bear upon the germ-plasm until after 

 the second or third division following the 

 reducing divisions and are perhaps sepa- 

 rated from this act by a considerable 

 period of time. It will be necessary, there- 

 fore, to alter our present conception of 

 mutation, or to conclude that another form 

 of alteration in heredity has been dis- 

 covered. The former alternative seems 

 possible and preferable. The forms in- 

 duced may indeed have a eytological basis 



