SEXUALITY IN PLANTS—JOHNSON. BO 
1891), in @dogonium (Klebahn, 1892), in the plant rusts (Dangeard 
-and Sapin-Trouffy, 1893), in the toadstools (Wager, 1893), in the 
red alga Nemalion (Wille, 1894), in Spherotheca (Harper, 1895), in 
the rockweed, Fucus (Farmer and Williams, 1896). Finally Zeder- 
bauer (1904) reported it for the Peridines, and Jahn (1907), Olive 
(1907), and Kraenzlin (1907) made it out in the myxomycetes. 
The observations just referred to, and many others on plants in all 
groups, warrant the general application of Strasburger’s conclusion 
that a nuclear union is the characteristic feature of every sexual 
process. The few cases where the male cytoplasm seems more promi- 
nent than usual, as in the three conifers studied by Coker (1903), 
Coulter and Land (1905), and Nichols (1910), can not yet be said to 
have rendered it very probable that this cytoplasm plays a primary 
part as an inheritance carrier. 
IV.—-THE DISCOVERY OF THE ALTERNATION OF GENERATIONS IN 
PLANTS, 1851. 
The fact that the sexual cells of the higher plants are produced on 
a plant body or individual distinct from that which forms the asexual 
reproductive cells, and that in the normal life cycle the one type of 
individual arises from, and later gives rise to, an individual of the other 
type, must be regarded as one of the most significant features of the 
evolution of plants yet discovered. One of the chief general results of 
te magnificent work of Hofmeister was the discovery of this regular 
alternation of a sexual and an asexual generation, not only in the life 
history of the mosses and ferns, but also in that of the seed, plants. 
Hofmeister states this result clearly in the Vergleichende Untersuchun- 
gen, and makes it apply still more broadly in a brilliant generalization 
published in the Higher Cryptogamia. There he says (p. 439): 
The phenogams, therefore, form the upper terminal link of a series, the members of 
which are the Coniferze and Cycadez, the vascular cryptogams, the Muscinez and the 
Characeze. These members exhibit a continually: more extensive and more inde- 
pendent vegetative existence in proportion to the gradually descending rank of the 
generation preceding impregnation, which generation is developed from reproductive 
cells cast off from the organism itself. 
Since Hofmeister’s day detailed investigations by many workers 
have fully confirmed Hofmeister’s conclusion. They have shown the 
essential homology, not only of the spore-producing organs, and the 
one or two kinds of spores produced in them, but also of the structures 
arising from these spores, throughout all cormophytes, from the mosses 
upward. 
In the studies of the alge that followed immediately after Hof- 
meister’s work, investigators of these plants sought in them for some 
evidence of that regular alternation of sexual and asexual phases that 
had been demonstrated in higher plants. Pringsheim (1856, p. 14) 
