1915] 



MACDOUGAL — MODIFICATION OF GERM-PLASM 271 



perience of these cells are not reflected back to the embryonic 

 tract, so far as available facts may be considered. Sexually 

 specialized reproductive elements with a reduced number of 

 chromosomes are developed from the embryonic tracts in a 

 late stage of the ontogeny, and these elements present a meta- 

 bolic balance different from that of the meristem stage, the 

 colloids having a greater density, and some of the energy 

 transformations having altered velocities. 



The embryonic tract or meristem of a higher plant at any 

 given moment includes an enormous number of primitive or 

 initial cells and of separating elements in all stages of division, 

 growth, and differentiation toward the specialized tissues 

 which are derived from it. The tract as a whole could there- 

 fore not react in a unified manner to any climatic or environic 

 agency which would impinge upon the plant. Such forces, as a 

 matter of fact, visibly affect only the manner in which the dif- 

 ferentiation of the resting tissues takes place. The rejuven- 

 escence of such differentiated cells might carry the effects into 

 the organ or individual produced by the regeneration, but no 



test has yet been made of this matter, or of the transmission of 

 such supposititious characters to a second sexually produced 

 generation; neither has the proposal, that repeated or long 

 continued exposure of the germ-plasm to any environic stimu- 

 lus may result in the fixation of effects, been tested out. The 

 continuation of introduced species in the mountain, desert, and 

 coastal plantations of the Department of Botanical Research 

 for the term of years during which any one person might con- 

 duct such experiments, may not be taken as an adequate test of 

 this phase of the matter, although these cultures are carried on 

 for the express purpose of determining what permanent 

 changes may be induced by the tension of unusual environic 

 complexes. So far these have been confined to alterations in 

 sexual and asexual reproductive procedure, and to alterations 

 in structure and aspect of the shoot, while no tests have been 

 made upon the fixity of the changes. 



Aberrant behavior of the chromosomes in certain determi- 

 native or initial cells may possibly be responsible for bud- 

 mutations or bud-variations, and theoreticallv it is conceivable 



