118 NATURAL SCIENCE [August 
divisions producing the sexual-cells. In Metaphyta, there are two 
such alternating cycles of colonial and protistoid growth, the Moss- 
Plant or Fern-Scale producing the sexual cells, and the Moss-Urn or 
Fern-Plant producing the asexual spores. In 1891, I wrote of nuclear 
reduction :—‘“ We may perhaps regard it as an adaptation to prevent 
the undue multiplication of chromatomeres in the zygote, and the 
cells produced therefrom.’ This view has been elaborated by Stras- 
burger; but it will be better, as we shall see, to explain it in another 
form than his. As, normally, each nucleus exhibits on its division 
the same number of segments that it had on its formation; the 
fertilised ege, oosperm, zygote, or whatever we please to call a cell 
formed by the fusion of two, on its division will present twice the 
number that were present in either of its two original constituents. 
If, then, at each sexual fusion this doubling continued, the number of 
nuclear segments in each cell would increase indefinitely in geometric 
progression, which is, of course, out of the question: a reduction must 
take place somewhere. This'necessary reduction takes place at the 
first resumption of protistoid multiplication. In Metaphyta, 
where there are two such resumptions, this is obvious; in Metozoa 
there is only one such resumption, which coincides with the forma- 
tion of the (protistoid) sex-cells, and it is this mere coincidence 
that gave rise to the idea that reduction was a preparation for 
cell-fusion, instead of being the necessary consequence of 
cell-fusion. 
A very curious case is that of Fucus, the Bladder-Wrack, which, 
like an animal, has only one colonial form—the familiar plant, and 
one protistoid reproduction, that producing the sexual cells; here, 
as we should anticipate, reduction occurs as in Metazoa at the incep- 
tion of the latter process. Had this case been worked out before 
that of the Vascular Cryptogams, it would have afforded great support 
to the physiological hypothesis. 
Again, the little fresh-water Algae, the Conjugatae, have their 
cells isolated, or at most in simple colonies of filaments, where the 
cells, placed end to end in a single row, divide each on its own 
account, so that they are really rather protistoid than comparable 
with the differentiated colonial cells of higher plants. In these 
plants nuclear reduction occurs at yet another point of the cycle, 
namely, at the very first cell-divisions of the zygospore, which is, as 
we see, the resumption of protistoid cell division after conjugation. 
Strasburger’s statement of this explanation is somewhat dif- 
ferent. He writes: “The morphological cause of the reduction in 
number of the chromosomes ... is in my opinion phylogenetic. 
I look upon these facts as indicating a return to the original 
1 I pass by exceptional cases where the reduction occurs at a very early period in 
the cells of the ovary. 
