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 Lilium, 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 Nägeli, 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 (:05, pp. 246-252) presents an admirable 
. analysis of these problems. 
