Chromosomes in Pollen Mother-cells. 
339 
then all pangens are not alike. There is no definite evidence, as yet, 
among plants that any particular chromosome is entirely different from 
others, but there is at the same time every reason to believe that each 
gamete may contain all, or nearly all, of the parental qualities. It is also 
probable that these qualities are present in different degrees of potentiality 
in the different chromosomes. The theory of sex determination developed 
in the insects (Wilson, ’ 06 , and others) cannot be applied with equal force 
to plants, for no accessory chromosome, or probable sex determinant, has 
been observed in the plant kingdom. We may, however, reasonably 
attribute to the chromosomes in plants certain different qualities falling 
within narrow limits, and such an assumption may be based upon observed 
facts. It is seen that, in the spirem in which the individual chromomeres 
are demonstrable (Figs. 25, 25#), all of these are not paired, especially in 
the case of the smaller ones. The probabilities are that these smaller 
granules may become a part of one chromosome or another according to 
the rules of chance, or according as certain qualities of a group have 
a stronger affinity for each other than for others. If we are in any way 
justified in ascribing some individual quality or qualities to these apparently 
unpaired granules, then we are justified in concluding that some chromo- 
some or chromosomes are to that extent hereditarily different from others. 
Otherwise, what value can a reducing division have further than that of a mass 
reduction ? Of course, we may say also with a large degree of probability 
that the nuclei of the gametophyte differ from those of the sporophyte 
only in the amount of hereditary substance, and not a difference in the 
hereditary qualities of that substance. 
In regard to placing any great significance in the fact that in some 
plants certain chromosomes are smaller and some larger than others, it 
seems to me that the constancy of such difference is not sufficient to 
warrant any definite conclusion at present, especially when the source of 
error in estimating the size of the chromosomes is considered, and also 
in the additional fact that, in many plants, one of the most conspicuous 
things is the difference in size of the chromosomes in similar cells. If we 
transfer the idea of individuality from the chromosome to the pangen, the 
significance of difference in size seems to be greatly diminished. In this 
connexion the question of the significance of the number of chromosomes 
in any plant arises. Why should one plant reveal only sixteen chromo- 
somes, another twenty-four, and still others larger numbers ? In Podo- 
phyllum and L ilium, which possess relatively large cells and a large amount 
of chromatin, we have relatively small numbers but large chromosomes. 
In other plants, as perhaps in the majority of Dicotyledons, there are 
usually smaller cells, a smaller quantity of chromatin, and a relatively large 
number of small chromosomes. Just what relation may exist between the 
size of the cell, the mass of chromatin, and the size and number of chromo- 
