Marcu, 1909] THE ORCHID REVIEW. 71 
These changes have been accompanied by the gradual and progressive 
degradation of the sexual stage, or gametophyte, through countless genera- 
tions of individuals—alga, moss plant, fern prothallus, pollen and ovules of 
flowering plants—and the corresponding increase of the asexual stage, or 
sporophyte—the moss fruit, fern plant, and the enormously developed 
vascular system of flowering plants. The gametophyte has not developed 
a vascular system. The latter change began with the adoption of a land 
habit by plants that were formerly aquatic, and is due to the totally different 
environmental conditions. This high degree of specialisation has been 
accompanied by an increasing provision for the protection of the germ cells, 
and their nutrition within the body of the second generation, by which they 
are withdrawn from allexternal influences. But both are phases of the same 
cycle, and produce each other alternately. The cycle has been continuously 
and progressively enlarged by the addition of new phases of development, 
and the modification of existing ones, but all are phases of the same cycle, 
and are subject to the laws which gave them birth. 
The individual cycle is a kind of recapitulation of the phases through 
which countless generations of the ancestors of an organism have passed in 
their evolutionary history, back to the most remote stages, and their 
permanence is due to what is known as the law of heredity, which is a kind 
of inertia, compelling an organism to follow a certain path or line of least 
resistance until diverted by the operation of changed conditions. Growth 
and reproduction are inseparable properties of living protoplasm, but are 
limited and directed by the conditions mentioned. Phases of development 
are only manifestations of the forces that are at work—sign-posts along the 
path of progress, whether we call them Mendelian units or not. Unit 
characters are supposed to be in some way bound up with what is termed 
the ‘‘germ plasm,” but even the germ plasm is a phase of development, 
whose beginnings can be traced, and neither the one nor the other are 
independent of the great law of evolution. 
Species may be considered to be organisms whose characters have 
become stable through having followed the same cycle of existence for 
numerous successive generations, such cycle being different, 7m some respect, 
from that of any allied species, and the phrase in italics is used intentionally, 
for it is held that allied species follow the same path during part of their 
course, deviating therefrom at certain definite points in response to some 
change in the environment. 
Hybrids are, or may be, unstable, because combining different hereditary 
tendencies, and as each tries to follow its own course, there is a struggle for 
the ascendancy, which may result in a compromise, or the stronger force 
may prevail, hence the various phases of dominance so often witnessed. The 
nature of the compromise may differ greatly according to the degree of 
