56 INTRODUCTION. 
number persists, and whether in the egg-cell this number obtains was 
not determined.’ 
As is well known, two views are held concerning the manner in 
which the reduction in the number of chromosomes is accomplished. 
One of these views, which has been given prominence by Weismann, 
holds that the chromosomes are qualitatively different, and that reduc- 
tion is accomplished during the maturation divisions in animal cells 
and in the first two divisions taking place in the spore mother-cells of 
higher plants. For example, in the second maturation division of the 
animal egg it is maintained that the daughter chromosomes do not arise 
as a result of a longitudinal splitting, but by a transverse division, or 
what is known as a qualitative division. The nuclei of the four cells 
thus resulting, whether representing the egg and its polar bodies or 
those which develop directly into spermatozoa, are hereditarily different 
in character, and it is upon this assumption that hereditary variation is 
based. 
The other view, which is now very generally accepted by botanists, 
is that, in plants no qualitative division exists, but the chromosomes 
of each mitosis arise in every case by a longitudinal splitting. The 
reduction takes place in the resting nucleus or during the early pro- 
phase of the first, or heterotypic, mitosis in the spore mother-cell of 
higher plants. The fact, as shown in preceding paragraphs, that 
during this first mitosis a double longitudinal splitting of the chromo- 
somes occurs, probably as a preparation for the two divisions, has led 
to much confusion, because these divisions were supposed to have been 
rather the instrument of reduction than a consequence of reduction. 
Assuming the persistent individuality of the chromosomes, we may 
conclude on good grounds that the reduction represents the actual and 
complete fusion of the chromosomes of both parents, which have 
remained separate in the sporophyte until the formation of the spore 
mother-cells. There is no visible evidence that a qualitative difference 
exists between the chromosomes in plants, and our assumption here is 
that they are hereditarily similar, because of the fact that every indi- 
rect nuclear division is preceded by a longitudinal splitting of the 
chromatin. 
Since the nucleus is the unquestionable bearer of hereditary char- 
acters, fusion of sexual nuclei in fecundation has for its purpose 
the blending of two lines of descent and possibly the restoration 
+J. Lloyd Williams in a recent paper (Studies in the Dictyotacez, Ann. Bot., 18; 141-160, 1904) 
observes facts that seem to point to the conclusion that the plantlets developing from the tetraspores, 
with their reduced number of chromosomes, may become gametophytes, and that the fecundated egg 
cells probably develop into tetraspore plants which have been shown to possess the increased number 
of chromosomes. If this be true, an alternation of generations exists in Dictyota. 
