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merous as the chromosomes of the somatic cells and often differ 
widely from them both in shape and size. 
The entire question of reduction rests upon the manner of 
tetrad-formation, but unfortunately, observers are diametrically 
opposed in their descriptions of the process. On the one hand it 
has been shown beyond question, that in some cases (the copepod 
crustacea) two of the four parts of the tetrad are formed by longi- 
tudinal division of the spireme-segment, while the other two arise 
by transverse division. In such cases two successive mitoses 
divide the tetrads, first into two dyads and second into single 
elements. By these two divisions the resultant reproductive cell 
receives one-fourth of each of the original tetrads. On the other 
hand, in another case, Ascaris megalocephala, where the facts also 
seem to be beyond contradiction, Brauer has shown that the tetrads 
arise by double longitudinal division of the spireme-segments and 
that no transverse division takes place. In this case reduction is 
purely quantitative and not qualitative. 
The botanists Guignard (1891) and Strasburger (1888) have 
maintained that in plants also, a reduction in the Weismann sense 
does not take place. Neither Guignard nor Strasburger found 
tetrads, They described the spireme as breaking up into half the 
normal number of chromosomes which undergo simple longitu- 
dinal division at each successive mitosis. 
It would be remarkable if a process so general in animal cells 
as the formation of tetrads should not be found in plant cells, and 
with the hope of finding some evidence of this in plants I under- 
took the study of reduction in the group of Pteridophytes, the re- 
sults of which are given in the following section. 
I. OBSERVATIONS. 
Guignard and Strasburger found that in Zz/iwm and in Allium 
the pollen-grain after reduction, undergoes subsequent mitoses, 
in each of which the same reduced number of chromosomes is re- 
tained. This led Overton (1892) to suggest that reduction in the 
higher cryptogams, where sexual and asexual generations alternate, 
might take place as far back as the formation of the spore. . He also 
suggested that all of the cells of the sexual generation might have 
the reduced number of chromosomes, and in 1893 he strength- 
