May, 1905.] The Nature of the Reduction Division. 
337 
gametophytes with a true alternation of generations they are 
retained in the ovary. The plant life cycles together with a 
typical animal are compared in Plate XXL 
Among the interesting things which have recently come to 
light and which appear to have their basis in the phenomena of 
the reduction division is Mendel’s law of heredity in hybrids. 
The operation of this law can be explained on the hypothesis of 
pure sex cells. In 1897 the writer worked out in detail the 
reduction division which takes place in the ovule of Lilium 
philadelphicum. Although the development and subsequent 
division of the chromosome was followed out in considerable 
detail in this work, the facts presented were not accepted by a 
number of botanists, as admitted by Strasburger, because of 
supposed authority in the opposite direction. So soon, however, 
as Mendel’s law was rediscovered it became self-evident that 
belief in a qualitative or true reduction division of some kind was 
necessary if the whole chromatin hypothesis was not to fall to 
the ground. Accordingly a re-investigation by some of the fore- 
most cytologists, among them Strasburger and Farmer, resulted 
in a conhrmation and acceptance of the propositions presented 
in my papers on Lilium and Erythronium, as also of similar work 
done previously by a number of zoologists. 
Fig. 3. Diagramatic representation of the transverse division of a 
chromosome. 
If then a transverse division of the chromosomes occurs dur- 
ing the reduction karyokinesis each of the chromosomes resulting 
from the process of pseudo-reduction may be regarded theoret- 
ically to be made up of a pair of chromosomes, one being a male 
chromosome and the other a female chromosome, joined end to 
end. There are also some obrsevations which appear to indicate 
that this actually takes place. In such cases then as in Lilium 
and Erythronium the formation and nature of the twisted loop 
can be diagramatically represented as in Fig. 3, a-e. In the fol- 
lowing division in which a longitudinal splitting occurs the 
daughter halves of the chromosomes formed early in the previous 
division become separated (Fig. 3, f-h). 
Mendel’s law of heredity, so far as it has a direct bearing on 
the nature of the reduction division, may be briefly stated as fol- 
lows: When two organisms differing in some character are 
