ORGANIZED DEVELOPMENT IN PLANTS
43
umes following international plant tissue culture conferences. These volumes include the volume of the Briançon conference edited by Gautheret
(1954, 1955), the Woodstock conference edited by White (1957), and
the Delhi conference edited by Maheshwari (Maheshwari and Ranga
Swamy, 1963). The publication from the conference at Pennsylvania State
University in 1963 has been edited by White (1965). Related papers
appear in the book edited by Skoog (1951), in the Brookhaven Symposia
No. 6 (Sparrow, 1954) and No. 16 (Miksche, 1964), and in the Society
for Experimental Biology Symposia No. 11 (Porter, 1957) and No. 17
(Fogg, 1963). The volume edited by Lang (1965) on differentiation and
development dwells on many aspects simply touched upon here.
II. The Development of Embryonic Structures
A. Embryogenesis in the Flowering Plants
The prime place to study the initiation of organized development in
plants is in the fertilized egg. Here is first formed the unified diploid
genome in a cytoplasm which has the potential and normally does give
rise to the whole new individual. The zygote passes progressively through
recognizable embryonic morphological stages from a single cell to the
mature embryo and, thence, under appropriate environmental stimuli to
the adult organism. To follow the fertilized egg or zygote from its singlecelled state through embryonic development is to follow at the cellular
level the initiation of multicellular organization. This is why there exists
the great interest and vast literature on the embryology of the angiosperme (refer to classic and modern references, e.g., Maheshwari, 1950,
1963b; Johansen, 1950; Wardlaw, 1955; Souèges, 1951; Schnarf, 1931;
Crete, 1963; and many others).
To describe precisely and in detail the ontogeny of cellular changes
during development is a first step in understanding the initiation of
organization. In the angiosperms, an elaborate structural mechanism has
evolved as part of the protection of the embryonic process. Embryogenesis proceeds inside a complex investing structure—the ovary, which
contains within it the complicated layer-upon-layer structure of the
ovule with its integuments, nucellus, and embryo sac. The single-celled
embryo is buried deep within the maternal tissues in the embryo sac and
is surrounded by an elaborate organic nutriment upon which it depends
for its survival to embryo maturity. The variations upon this general
structural theme in the angiosperms are manifold and have been described in detail for many species by the use of light microscopy and
histological sections. From such studies it is apparent that, at the time
of fertilization, two gametic fusions typically occur—one sperm nucleus
43
umes following international plant tissue culture conferences. These volumes include the volume of the Briançon conference edited by Gautheret
(1954, 1955), the Woodstock conference edited by White (1957), and
the Delhi conference edited by Maheshwari (Maheshwari and Ranga
Swamy, 1963). The publication from the conference at Pennsylvania State
University in 1963 has been edited by White (1965). Related papers
appear in the book edited by Skoog (1951), in the Brookhaven Symposia
No. 6 (Sparrow, 1954) and No. 16 (Miksche, 1964), and in the Society
for Experimental Biology Symposia No. 11 (Porter, 1957) and No. 17
(Fogg, 1963). The volume edited by Lang (1965) on differentiation and
development dwells on many aspects simply touched upon here.
II. The Development of Embryonic Structures
A. Embryogenesis in the Flowering Plants
The prime place to study the initiation of organized development in
plants is in the fertilized egg. Here is first formed the unified diploid
genome in a cytoplasm which has the potential and normally does give
rise to the whole new individual. The zygote passes progressively through
recognizable embryonic morphological stages from a single cell to the
mature embryo and, thence, under appropriate environmental stimuli to
the adult organism. To follow the fertilized egg or zygote from its singlecelled state through embryonic development is to follow at the cellular
level the initiation of multicellular organization. This is why there exists
the great interest and vast literature on the embryology of the angiosperme (refer to classic and modern references, e.g., Maheshwari, 1950,
1963b; Johansen, 1950; Wardlaw, 1955; Souèges, 1951; Schnarf, 1931;
Crete, 1963; and many others).
To describe precisely and in detail the ontogeny of cellular changes
during development is a first step in understanding the initiation of
organization. In the angiosperms, an elaborate structural mechanism has
evolved as part of the protection of the embryonic process. Embryogenesis proceeds inside a complex investing structure—the ovary, which
contains within it the complicated layer-upon-layer structure of the
ovule with its integuments, nucellus, and embryo sac. The single-celled
embryo is buried deep within the maternal tissues in the embryo sac and
is surrounded by an elaborate organic nutriment upon which it depends
for its survival to embryo maturity. The variations upon this general
structural theme in the angiosperms are manifold and have been described in detail for many species by the use of light microscopy and
histological sections. From such studies it is apparent that, at the time
of fertilization, two gametic fusions typically occur—one sperm nucleus