Notes on Recent Literature. 
214 
Medlar, the internal tissue being derived from the White-thorn. 
Daniel’s 1 observations indicate that his Pear-Quince hybrid is also 
a periclinal chimaera, with the Pear internal. 
The phenomenon, so common among these periclinal chimaeras. 
of the spontaneous production of reversionary shoots appears to be 
due to some irregularity in the divisions of the meristem, the cause 
of which is unknown. The change of form often exhibited by the 
adventitious shoots produced as a result of wounding, seems to 
follow naturally enough upon the opportunities for a rearrangement 
of the components which are afforded by the death of certain cells 
and the rapid multiplication of others. 
There remains one of Winkler’s intermediate types w r hich 
suggests further possibilities. Winkler finds that the germ-cells 
of this type (S. Darwinianum) possess twenty-four chromosomes, 2 
the reduced number of the Tomato being twelve, that of the 
Nightshade thirty-six. Winkler therefore supposes that in this case 
a fusion must have taken place between the vegetative cells of the 
pure species, and that the sub-epidermal layer of the hybrid, at 
least, must be the product of this fusion. 
At one time some acceptance was accorded to the idea that 
graft-hybridism, if it were a real phenomenon, must involve cell- 
fusions between the graft-symbionts. But the cytological studies 
of Strasburger 3 and Noll 4 lent no support to the hypothesis, the 
graft-hybrids which were examined being found to possess the same 
number of chromosomes as their respective parents ; and though 
Nemec suggested that an autoregulative process of reduction might 
take place, whereby the diploid number of chromosomes would be 
restored, there was little positive evidence in favour of his suggestion. 
Further investigations into the origin of 5. Darwinianum will 
be awaited with great interest, for at the present time it alone 
affords any positive indication that such cell-fusions may take place, 
giving rise to cells, and ultimately to tissues, which are essentially 
of a hybrid nature in contra-distinction to the tissues of a chimaera, 
which are pure to one species or the other. 
Of the literature cited below, the works of Darwin, Strasburger 
and Noll provide general descriptions of the characters and 
putative origin of the earlier graft-hybrids; in them will be found 
references to a number of articles wrhich need not be recapitulated 
here. 
R.P.G. 
1 Daniel (5). 
2 Winkler (15). 
3 Strasburger (10). 
4 Noll (8), p. 37. 
