116 



The Journal of Hereditv 



are always thinner than leaves of wild 

 cxaltata grown under identical condi- 

 tions and differ further in that they 

 produce no fertile sporangia. 



Two points are of special interest 

 in connection with these plants reported 

 by Air. Simpson : 



First, that a rather delicate, green- 

 house variety of Boston fern, 

 JVhituiani, has maintained itself and 

 increased over a period of twelve years 

 under conditions of natural competition. 



Second, that the i)lants have retained 



an approximation of the typical form 

 of the leaf. Given hest greenhouse 

 conditions, it is almost certain that 

 these naturalized plants would show 

 the typical plume tyi)e of the normal 

 JVIiitniaui. 



If any reader is in a position to 

 make a more extended, test of other 

 varieties, I shall he glad to send a 

 selection, including some new, un- 

 named types, which would answer all 

 the requirements of specific distinction, 

 according to descriptive taxonomy. 



FURTHER POINTS ON THE RELATION 

 OF CYTOLOGY AND GENETICS* 



P. W. Whiting 



lo-a'a Child JVcIfarc RcscarcJi S fat ion. 



IN VIEW of the recent announce- 

 ment of G. H. Shuir't that he has 

 actually found crossing over in 

 Oenothera, the remarks of R. Rug- 

 gles Gates^ in reference to the cyto- 

 logical conditions should be consid- 

 ered. Gates (p. 76) states, "As is well 

 known, in Oenothera the chromosomes 

 form a chain end-to-end like a string 

 of sausages, and when they ultimately 

 come to be side-by-side in diakinesis 

 they are already in the short and stout 

 condition in which twisting about each 

 other is impossible. This is a very 

 disturbing fact for those who write 

 about 'crossing over' in Oenothera." 

 Just why geneticists should be dis- 

 turbed by an end-to-end arrangement 

 of sausage-like chromosomes I am un- 

 able to understand. It is obviously up 

 to those who insist on some other ex- 

 planation of crossing over than that 

 usually held, to show that these sau- 

 sage-shaped chromosomes are of the 

 same constitution as those that en- 

 tered into synapsis. The fact that the 

 diploid number should occur in late 



prophase preceding the first matura- 

 tion or heterotypic division throws no 

 light upon the stages when crossing 

 over occurs. 



Crossing Over in Fine Thread Stage 



Plough^ (p. 187) from temperature 

 experiments with Drosophila, has 

 shown that crossing over occurs at a 

 very early stage when the chromatin 

 threads are extremely tenuous, "in 

 what resembled a late leptotene or 

 early diplotene condition in other 

 forms." Such stages have not as yet 

 been adequately studied in Oenothera. 

 Refering to this genus in an earlier 

 paper' (p. 11) Gates writes, "in the 

 earlier stages . . . .parallel threads 

 could not be observed, and it has not 

 been determined whether they were 

 really absent or whether the failure to 

 observe them was due to their ex- 

 treme delicacy." W'enrich's^ careful 

 studies on leptotene and zygotene 

 stages in spermatocytes of the grass- 

 hopper, Phrynotettix, which is evi- 

 dentlv verv favorable material, have 



* A reply to "Some Points on the Relation of Cytoloo;y and Genetics," by R. R. Gates, 

 in The Journal of Heredity for February, l<t22. 



t For Numbered References, see Literature Cited, at end of article. 



