103 
Some Recent iVork on Hybrids in Plants. 
0 
also stated, that of a pair of characters, the one which is phylo- 
genetically the older is usually either the stronger or dominant; this* 
however, is not universally true. It would seem that the whole 
question as to the relation of the characters of the hybrid to 
the ancestry of the parents can only be settled by further 
observations. 
In conclusion, a few remarks must be made concerning the 
interesting work of Correns on Xenia in Maize, and on the question 
of the probable time and mechanism of separation of the characters 
of schizogonous pairs. 
Correns’ observations on hybrid Zea-mces were originally under¬ 
taken in 1897 with the object of studying the direct effect of pollen 
on the fruit, or Xenia as it has been called by Focke, for which the 
Maize races, with their endosperms of various colours and natures, 
were obviously well suited. It was very soon clear the influence of 
the pollen, apart from that on the embryo, was confined to the 
endosperm alone, but in that structure its effect was very striking* 
There seemed to Correns at the time only two probable theories 
to explain this influence ; either that the endosperm arose from a 
sexual fusion, or else that there was some ferment-action by the 
hybrid embryo on the endosperm. As there was not the least 
histological evidence for the first theory, Correns inclined towards 
a belief in the second. The discovery, however, of double fertili¬ 
zation by Nawaschin and Guignard in 1899 gave the necessary 
proof that the endosperm also was of hybrid nature, and showed 
the correctness of the first hypothesis. Recently the latter observer 
has proved the existence of double fertilization in Zea Mays itself. 
The direct influence of the pollen is most striking in the colour of 
the aleurone-layer and endosperm, and in the chemical nature of the 
reserve material. As was stated earlier, starch was found to 
be dominant over sugar whichever way the cross was made, but 
in the o^her two categories, the endosperm, though intermediate 
in character between the parents, much more strongly resembled 
the female parent. Further, in the case of the form of the cells of 
the aleurone-layer (whether long or short), foreign pollen had no 
effect at all in the first generation, though this pair of characters 
was obviously homodynamic, as later generations showed. It is 
thus clear that there is a striking general tendency for the hybrid 
endosperm in the first generation to resemble more strongly the 
female parent. The simple explanation put forward by Correns is 
no doubt the correct one, that, as the hybrid endosperm is derived 
