viii Translator's Preface 



manently removing the entire question of organic evolu- 

 tion from the realm of ineffective speculation, and estab- 

 lishing it upon the firm basis of experimentation. 



The term pangen is employed in its original sense by 

 Strasburger in his paper on "Typische und allotypische 

 Kertheilung." 5 



Recognizing the existence of some material entities 

 as the ultimate units of heredity, conceiving of them as 

 invisible, and accepting for them the name pangen, he 

 interprets the chromatin granules (chromomeres), which 

 can be directly seen, as larger or smaller pangen-com- 

 plexes, and suggests that we designate them "pangeno- 

 somes." The pangenosomes, owing to a "certain elective 

 affinity," he considers as combining into ids, (from the 

 idioplasm, of Nageli), and the ids, in turn, into chromo- 

 somes. 6 



Referring to de Vries's supposition, that the pangens 

 influence the cytoplasm by wandering out into it from the 

 nucleus and thus changing from an inactive to an active 

 state, Strasburger 7 records his failure to detect any visi- 

 ble evidence that the bodies which he calls pangens thus 

 wander out from the nucleus into the cytoplasm, but refers 

 to the period in cell-division when the nuclear membrane 

 disappears and the spindle forms, as serving to bring the 

 chromosomes into direct contact with the cytoplasm, and 

 thus establishing a condition favorable for the ''forma- 

 tive influencing" of the cytoplasts by the nucleoplasts. A 

 similar influence might also result from extranuclear nu- 

 cleoli distributed in the cytoplasm. In the fertilization 



5 Jahrb. Wiss. Bot. 42: 1-71. 1905. 



6 Mottier's use of the word pangen to designate the visible chro- 

 momeres (Ann. Bot. 21; 307-347. 1907.), employs the term in a 

 sense entirely at variance with that for which it was originally pro- 

 posed (cf. p. 49.) 



7 hc. cit. p. 74. 



