142 
The Ohio Naturalist. 
[Vol. XIII, No. 7, 
A CYTOLOGICAL LIFE CYCLE. 
Robert F. Griggs. 
The figures and diagrams which are usually presented to 
explain the nature and significance of the reduction division to 
beginners, although clear enough in themselves, often fail in 
their purpose because they do not take account of the fact that 
reduction is indissolubly bound up with fertilization. To give 
a clear conception of the significance of reduction it is necessary 
to present the whole life cycle. In many respects the fern is 
better suited than any other type for the representation of such 
a cytological cycle. The alternation of generations is obvious; 
the haploid as well as the diploid condition is evident; the an¬ 
tithetic processes of fertilization and reduction occur at opposite 
points of the life cycle and can thus be presented far more clearly 
than when reduction appears to be merely the “maturation of 
the germ cells.” 
The diagrams here presented are based on a hypothetical 
fern with four chromosomes in the sporophyte. The cytology 
is that of Ascaris* very little schematized. Each of the chro¬ 
mosomes of which two are represented as short and two long, is 
marked with a characteristic figure so that its permutations 
may be followed through the cycle. 
The best stage with which to begin is the diploid mitosis of the 
sporophyte, which conforms to the familiar type of somatic karyo- 
kinesis generally described. Omitting the resting nucleus the first 
stage in division is the formation from the chromatin network 
of a long, continuous spirem which winds in and out more or less, 
filling the whole nuclear cavity (Fig. 1). Soon each granule of 
this spirem divides and it becomes double longitudinally (Fig. 2). 
After considerable contraction during which the chromatin 
granules are drawn closely together, the spirem breaks into 
four pieces, the chromosomes (Fig. 3). These are oriented on 
the spindle and divided longitudinally along the line of the early 
split (Fig. 4), one half going to each pole and entering into the 
corresponding daughter nucleus (Fig. 5), so that the progeny 
of every chromosome is equally divided between the daughter 
nuclei. As all of the cells throughout the organism arc produced 
in this manner each is exactly like every other in chromatin content 
and, on the hypothesis that the chromosomes bear the hereditary 
characters, in heritage as well. That this is actually the case 
in the heritage as well as in the chromosomes may be demon¬ 
strated by the familiar facts of vegetative propagation by which 
*See Griggs, R. F., A Reducing Division in Ascaris, Ohio Nat., 6' 519- 
527. 1906. Wilson, E. B., The Cell, 2d Ed., pp. 65-72, 183, 236-242. N. Y. 
1906. 
