No. 464.] STUDIES ON PLANT CELL.— VII. 583 



idioplasm may be separated so purely by the longitudinal split- 

 ting of the single (fusion) spirem or through the distribution of 

 unmodified sporophytic or somatic chromosomes as to give abso- 

 lutely and relatively pure germ cells through Mendelian laws. 



Allen's discussion, very briefly summarized above, is impor- 

 tant for the emphasis which is laid upon the significance of a 

 possible mixing of the parental idioplasms in the more or less 

 complete union of chromatic material, which is generally recog- 

 nized as characteristic of synapsis. There is a general tendency 

 to rest content when the chromosomes are accounted for as 

 units while they are merely the grosser form of expression of 

 the idioplasm whose final architecture is intricate far beyond our 

 present powers of analysis. Allen's own studies upon the events 

 of synapsis in the lily with the regular fusion in pairs of chromo- 

 meres of different parentage may well cause one to hesitate in a 

 full acceptance of the chromosome as fixed and unchanged in its 

 organic constitution throughout the life history. The phenome- 

 non of hybridization is far too complex to be explained in terms 

 of simple ratios and while some characters may be paired or 

 correlated in proportions that can be expressed by mathematical 

 formulae there is little probability that the assemblage of charac- 

 ters which make the species can be so definitely grouped as the 

 strongest disciples of Mendel may hope. However, a great 

 forward step has been taken and we may expect important 

 results from the empirical methods so clearly defined by Mendel 

 and by the close investigation that cytologists are making 

 of the history of idioplasmic structures (chromosomes) during 

 ontogeny. 



8. Xenia. 



Xenia is the " immediate or direct effect of pollen on the 

 character of seeds and fruits." The term was first proposed by 

 Focke, in 1881, and is now well estabhshed. Xenia has long 

 been known to the plant breeder as one of the most interesting 

 and puzzling problems of hybridization. The botanist has nat- 

 urally looked for the results ,of hybridization in the development 

 of the embryo from the seed since this structure has received 



