358 BOTANICAL GAZETTE [May 
The author substitutes for a period of mutation the conception of a nearly 
constant frequency of mutation. Thus, one plant in twenty of O. Lamarck- 
tana is a mutant, but only one in two hundred of O. biennis. In others there 
may be one in ten thousand or one in a million. 
Doubtless the most important fact presented is the result of investigations 
to determine the cause or causes of mutation. The introduction of strong 
osmotic and weak chemical solutions into the ovaries of Raimannia odorata 
shortly before fertilization, appears to have produced a large number of individ- 
uals of a hitherto unknown type. These new plants have a shorter life-cycle 
than that of the parent and are profoundly different in many characters. ey 
have already bloomed and fruited, and obviously constitute a potential species. 
If this new species holds its characters in succeeding generations, this discovery 
will be one of far-reaching importance, as the first real clue to the causes which 
may effect mutative changes in plants—GrorGE H. SHULL. 
Graft-hybrids——Noit has made a careful morphological, anatomical, and 
cytological examination of the supposed graft-hybrids between Crataegus mono- 
gyna (stock) and Mespilus germanica (scion) in the Dardar Garden at Bron- 
vaux near Metz, Germany.'3 Three branches, starting from the callus where 
stock and scion meet, present unmistakable evidence of their hybrid origin, each 
branch showing a different combination of the parental characters. 
A consideration as to the possibility of graft-hybrids, in the light of present 
knowledge of the behavior of the hereditary substance, leads to the conclusion 
that they must originate through nuclear fusions in the callus or not at all; and 
moreover, that the studies of NEMEC upon asexual nuclear fusions gives a basis 
of observed fact which warrants the affirmation that graft-hybrids are possible. 
The cytological examination of the several hybrid branches showed that their 
cells do not possess double the normal sporophyte number of chromosomes; there- 
fore, if these hybrids originated from the fusion of two vegetative cells, this process 
must have been followed by some method of chromosome reduction. This pre- 
sents no insurmountable difficulty, since NEMEC found that after 78 hours no 
nuclei were found which had more than the normal number of chromosomes, 
though many such were observed soon after fusion. 
The greater resemblance of one of the hybrids to Mespilus, and of the other 
two to Crataegus, and the change of one of the latter from nearly typical Cra- 
taegus to near one of the other hybrid forms, are explained by assuming that in 
each fusion one nucleus remained in its accustomed cytoplasmic surroundings, 
and that the other nucleus, moving into unaccustomed surroundings, w 
weakened or injured that, when the degeneration took place which reduced the 
romosomes to their normal number, the weakened or injured chromosomes 
contributed the fewest determinants to the hybrid nucleus, thus giving the hybrid 
13 Nott, T., Die Pfropf-Bastarde von Bronvaux. Sitzungsber. Niederrhezin. 
Ges. f. Natur-u. Heilkunde Bonn, 1905. Separate, 34 pp. 
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