No. 463.] STUDIES ON PLANT CELL.— VI. 499 



It is possible that they may be grouped in pairs (bivalent chro- 

 mosomes) either side by side through two parallel threads 

 (paternal and maternal spirems) or end to end in a single chro- 

 matic thread. But it will certainly be interesting if animals and 

 plants both show variations in these respects and very remark- 

 able if the same genus, as Lihum, should present contrasting 

 types of reduction phenomena. And on these points must be 

 concentrated the future investigations in this field. 



While we are making progress in our understanding of the 

 behavior of the chromosomes it must never be forgotten that in 

 them we are dealing only with the most conspicuous form of 

 germ plasm and that there are much finer elements which in 

 their turn will demand attention. We may hold to the view of 

 the individuality of the chromosomes as morphological entities 

 but nevertheless we must recognize the fact that the substance 

 of these bodies which stand for parental characters, the idioplasm 

 of Nageli, may pass through remarkable changes which are far 

 from understood. There is much evidence that the parental 

 idioplasm may mix or combine during synapsis in the organiza- 

 tion of the spirem from which are developed the reduced num- 

 ber of bivalent chromosomes. Allen has described the actual 

 fusion of sets of chromomeres believed to be of maternal and 

 paternal origin and there are many possibilities of the two idio- 

 plasms reacting upon one another to bring about intimate and 

 fundamental interrelations. These become important principles 

 in discussions of heredity and hybridization and will be con- 

 sidered later. Allen (:o5, pp. 246-252) presents an admirable 

 analysis of these problems. 



