SEXUALITY IN PLANTS—JOHNSON. 3938 
origin of the leafy fern sporophyte from a liverwort-like thallus Scott 
says (1911): 
We know plenty of intermediate stages between a thallus and a leafy stem; but no 
one ever saw an intermediate stage between a sporogonium and a leafy stem. 
V. THE DISCOVERY OF CHROMOSOME REDUCTION AND OF SYNAPSIS, 
1888. 
We have seen that during the two decades at the middle of last 
century students of sexuality in plants devoted their attention 
to the discovery of the relation of the pollen tube to the origin of the 
embryo. The three decades after 1860 were given largely to the 
proof of a union of a paternal with a maternal nucleus as a constant 
feature of the sexual process in plants. For the past two decades 
workers interested in reproduction have been engaged especially 
in determining the behavior and fate, in the various phases of 
plant development, of those essential elements of the nuclei, the 
chromosomes. The result of this study has been to give us a much 
more definite criterion than we had before of just what constitutes 
a sexual process. Moreover, this intimate examination of the 
chromosomes, together with the precise means of germinal analysis 
by breeding, introduced by Mendel, has given us some insight into the 
significance of the sexual process in the ontogeny and phylogeny of 
plants. 
The discovery of chromosomes in plants may best be attributed 
to Strasburger, who, in 1875, first figured them distinctly in the 
embryo of Picea. It is true that Hofmeister (1867) had noticed the 
equatorial plate of ‘‘albuminous clumps” in cells at the time of their 
division, and Russow (1872) saw, in the dividing spore mother- 
cell nuclei of Ophioglossum, plates of vermiform rods (‘‘Staébchen- 
platten”). Strasburger (1879), and Hanstein (1880), and Flemming 
(1880) were, however, the first to realize the constancy of the occur- 
rence of chromosomes in the dividing plant nucleus. The fact 
soon pressed itself upon the investigators that the number of these 
chromosomes differs in different plants and in different phases 
of the same plant. Then followed the epoch-making discovery of 
the zoologist Van Beneden (1883), that the number of chromosomes 
in the egg and sperm of the thread worm Ascaris is the same, and 
that the double number characteristic of the body cells becomes 
reduced during the maturing of the germ cells. Botanists after 
some delay, due, as Strasburger says, to lack of proper technique, 
succeeded in demonstrating these same facts for plants. Thus 
Strasburger in 1888 showed that the number of chromosomes char- 
acteristic of the egg and of the male nucleus in a number of angio- 
sperms is the same, and is fixed by a reduction occurring in the 
