TWENTIETH CENTURY EMBRYOLOGICAL CONCEPTS
29
accepted but attributed supreme significance to the developmental action
of the hereditary factors (see his "Theoretical Genetics," 1955, for an
exhaustive historical review); and he explained their developmental
functions specifically on the basis of enzyme activity (Goldschmidt,
1916) a number of decades before the propagation of the one-gene-oneaction theories (Beadle, 1945, 1949; Haurowitz, 1950) still so popular in
certain quarters, and long before Spiegelman (1948) was to evoke the
concept of competition for enzymes as explanatory of differentiation.
The fact remains, however, that the conceptual chasm between the
gene and the finally differentiated cell continues wide and deep, and
in spite of early beginnings by Wright (1916, 1945) it is only relatively
lately that successful progress is being made toward bridging it, with
the work for instance of Poulson (1940, 1945), Landauer (1948), Gluecksohn-Schoenheimer (1949), Gluecksohn-Waelsch (1951, 1953, 1954), and
Hadorn (1951, 1955), to mention only a few selected arbitrarily. When
biochemical steps intervening between the gene and its effect can be
followed (Ephrussi, 1942) or postulated (Landauer, 1954), the study
of development becomes itself molecular biology, although unfortunately
it must be remembered that the ultimate and really only significant step
leading directly back to the gene itself remains as yet to be followed for
metazoan material.
Goldschmidt, of all the students concentrating on heredity one of the
most acute in his intuitive and analytical understanding of embryological
problems, was one of those who recognized fairly early the possibility
that extranuclear as well as nuclear factors might be instrumental in
various ways in the regulation of differentiation (Goldschmidt, 1924,
1938; see also Part II of "Theoretical Genetics," 1955, which is devoted to
The Cytoplasm as Seat of Genetic Properties). For all his vision, however, and for all the emphasis placed on cytoplasmic inclusions by such
influential embryologists as Ε. B. Wilson, Boveri, and Conklin, any
postulate that differentiation might be controlled by extranuclear factors
in the genetic sense would have been viewed as wholly untenable, at
least on this side of the Atlantic Ocean, throughout by far the greatest
part of the first half of this century, as all of us will remember who are
more than 40 years of age. Had Spemann concluded his Silliman lectures
in 1933, for instance, by interpreting his results in terms of plasmagenes,
as Holtfreter and Hamburger (1955) have just now attempted, his
audience no doubt would have suspected him of showing signs of senility or something worse.
Goldschmidt (1955) has suggested that what has restored respectability in America to an interest in cytoplasmic inheritance has been the
29
accepted but attributed supreme significance to the developmental action
of the hereditary factors (see his "Theoretical Genetics," 1955, for an
exhaustive historical review); and he explained their developmental
functions specifically on the basis of enzyme activity (Goldschmidt,
1916) a number of decades before the propagation of the one-gene-oneaction theories (Beadle, 1945, 1949; Haurowitz, 1950) still so popular in
certain quarters, and long before Spiegelman (1948) was to evoke the
concept of competition for enzymes as explanatory of differentiation.
The fact remains, however, that the conceptual chasm between the
gene and the finally differentiated cell continues wide and deep, and
in spite of early beginnings by Wright (1916, 1945) it is only relatively
lately that successful progress is being made toward bridging it, with
the work for instance of Poulson (1940, 1945), Landauer (1948), Gluecksohn-Schoenheimer (1949), Gluecksohn-Waelsch (1951, 1953, 1954), and
Hadorn (1951, 1955), to mention only a few selected arbitrarily. When
biochemical steps intervening between the gene and its effect can be
followed (Ephrussi, 1942) or postulated (Landauer, 1954), the study
of development becomes itself molecular biology, although unfortunately
it must be remembered that the ultimate and really only significant step
leading directly back to the gene itself remains as yet to be followed for
metazoan material.
Goldschmidt, of all the students concentrating on heredity one of the
most acute in his intuitive and analytical understanding of embryological
problems, was one of those who recognized fairly early the possibility
that extranuclear as well as nuclear factors might be instrumental in
various ways in the regulation of differentiation (Goldschmidt, 1924,
1938; see also Part II of "Theoretical Genetics," 1955, which is devoted to
The Cytoplasm as Seat of Genetic Properties). For all his vision, however, and for all the emphasis placed on cytoplasmic inclusions by such
influential embryologists as Ε. B. Wilson, Boveri, and Conklin, any
postulate that differentiation might be controlled by extranuclear factors
in the genetic sense would have been viewed as wholly untenable, at
least on this side of the Atlantic Ocean, throughout by far the greatest
part of the first half of this century, as all of us will remember who are
more than 40 years of age. Had Spemann concluded his Silliman lectures
in 1933, for instance, by interpreting his results in terms of plasmagenes,
as Holtfreter and Hamburger (1955) have just now attempted, his
audience no doubt would have suspected him of showing signs of senility or something worse.
Goldschmidt (1955) has suggested that what has restored respectability in America to an interest in cytoplasmic inheritance has been the