152 CANNON: STUDIES IN PLANT HYBRIDS 
of nuclear division in it, may give grounds for interesting and | 
legitimate conclusions. It is of course only these general consid- 
erations that I can take up in the present paper. 
From the summary of Juel’s work on the Syrizga hybrid it 
was seen that all of the maturation divisions were more or less 
abnormal. What may perhaps be considered the nearest approach 
to the normal division observed in this hybrid was an apparently 
typical achromatic figure accompanied by many small chromosomes, 
which were therefore not like those of heterotypic nuclear mitoses, 
and which did not split in the metaphase. And it is of interest to 
note that Syrizga is probably a sterile hybrid. 
Turning now to the results of Guyer from the study of fertile 
hybrid pigeons, we note that he observed both normal and abnor- 
mal mitoses, and some mitoses which were not clearly the one or 
the other. The latter are of particular interest since it is primarily 
these that he considers a possible basis for the variation of hybrids. * 
Among the irregularities in the mitoses in fertile birds, which may 
contribute to variation, is the following. In the dividing nuclei of 
some secondary spermatocytes two spindles occur, each bearing 
half the somatic number of smal! chromosomes.} As previously 
given, Guyer concludes (1) that the two-spindle condition shows 
a tendency in the chromatin of each parent to retain its individu- 
ality, (2) that by a proper separation and distribution of the chro- 
mosomes pure sex-cells would result, and (3) that the union of 
these might cause reversion. This conclusion appears to have 
been drawn before the publication of the Mendelian law.t 
If the form of maturation mitosis just described occurs gen- 
erally in hybrids, and further if the chromatin is separated and 
distributed as postulated by Guyer, we should evidently not have 
to go further in order to discover the kind of mitosis that would 
produce in hybrids of the Piswm-type ‘‘ pure” germ-cells — the im- 
portant part of the Mendelian theory.§ There are however one or 
* Guyer. Science, I]. 11: 248. 1900. 
ft Compare Metcalf on hybrid G/adio/us, 7. ¢. 
{In his most recent paper (see footnote on p. 155) which was received after this 
was written, Guyer considers it possible that ‘* pure’’ reproductive cells may be derived 
trom normal mitoses, 
2 Bateson and Saunders, /. c. 12: ‘the essential part of the discovery is that //¢ 
germ-cells or gametes produced by cross-bred organisms may in respect of given charac 
ters be of the pure parental types.”’ 
