91 
The Nucleus and Heredity. 
Reduction seems to have no clear meaning apart from the prevention 
of the summation of hereditary material (possibly of organisation) 
which would be the result of consecutive processes of gametic union. 
A halving of the chromatin would seem to be quite unnecessary on 
ordinary physiological grounds, since the visible nuclear material 
may increase and decrease during the ordinary vegetative life of the 
cell. Fourthly there is the striking parallelism between the morpho¬ 
logical phenomena of the reduction-division and the facts of 
Mendelian segregation. Fifthly we have the general phenomena 
of gametic union ; for this process throughout the animal and 
vegetable kingdom, from the Protista to the highest animals and 
plants, is always characterized by a nuclear fusion, while the amount 
of cytoplasmic fusion varies greatly and is sometimes reduced to zero. 
The amount of protoplasm associated with the spermatozoon of 
animals is so small that it is of doubtful importance in heredity; it 
is most simply explained as mainly a motor-mechanism associated 
with the movement of the cell. In such forms as Paramcecium the 
two conjugating cells are united only by a narrow bridge of proto¬ 
plasm, and while there is an obvious nuclear interchange there is no 
clear cytoplasmic interaction. Again in the case of such Angio- 
sperms as Lilium and Helianthus, we have the observations (mostly 
neglected by zoologists) of Strasburger,' Nawaschin 2 and the 
writer, 3 which supply the critical evidence for the monopoly of the 
nucleus (at least in these cases) in the transmission of hereditary 
qualities. In these forms the male element is in no sense a cell but is 
a mere, naked nucleus of a spiral form and apparently self-motile. 
To these five important lines of evidence may be added the 
contrast between the simplicity of the processes of cell-division and 
the complexity of ordinary nuclear division. This points to the 
superior importance of the nucleus, as does the fact that in many 
cases large portions of the protoplasm can be broken from the egg 
without interfering with its capacity to develop, after fertilisation, a 
a normal embryo. Again the first few cells of a developing egg 
may be shaken apart from one another and each will develop into a 
small complete embryo, though the amount of protoplasm with 
which each starts may be only one-eighth part of the original proto¬ 
plasm of the egg. If there are in the protoplasm special carriers 
of the hereditary material, they must be repeated many times in 
1 Jahrb. f. wiss. Botan. Bd. 45, 1908. 
2 Oesterreichische Botan. Zeitschrift 1909, No. 12. 
3 Report of British Association, Sheffield 1910. 
