ORGANIZED DEVELOPMENT IN PLANTS
53
1963), from embryos of the orchid Vanda (Rao, 1963), and from callus
tissues derived from cultures of ovaries of the umbelliferous genus
Anethum
(Johri and Sehgal, 1963). Ranga Swamy (1961) also reported
the development of pseudobulbils from callus tissue derived from the
nucellar tissue of a Citrus species. Some interpretation of the origin of
these embryos from such callus tissues is given by Maheshwari and Ranga
Swamy (1963). One striking feature of several of these studies was that
adventive embryo formation seemed to be markedly stimulated by treatment of the embryos in culture with casein hydrolyzate.
Most dramatic have been the reports by Steward et al. (1964) and
Halperin and Wetherell (1964) in the United States and Kato and
Takeuchi (1963) in Japan that callus tissues derived from wild carrot
embryo, root or hypocotyl, cultured on a coconut-milk medium on agar
and then subcultured under different conditions, spontaneously differentiated bipolar embryos which even passed through the developmental
stages typical of ovular embryos of wild carrot. Steward found that
tissues derived from immature embryos placed in culture produced a
friable callus which could be cultivated in liquid coconut-milk medium
as a suspension. Such a cell suspension when plated out on the same
medium in agar plates formed thousands of carrot embryos in such
numbers as to demonstrate without direct examination that many
embryos were, in fact, derived from very small cell clumps and even
single cells. In the study by Halperin and Wetherell (1964), adult wild
carrot root was used to form the initial carrot callus, and from this
callus, cultured on a variety of complex media on agar, there developed
typical bipolar embryos. Recently Halperin (1964) has described some
of the effects of nutrients on embryo development in this system.
At the present time, greatest success in this direction has been
achieved with the wild strain of Daucus carota L.; several other members of the Umbelliferae tested in the same way have not shown the
capacity for embryo formation under these conditions (Halperin and
Wetherell, 1964). The greater tendency of callus derived directly from
embryos to form embryos readily (Maheshwari, 1963a; Steward et al.,
1964) suggests that in some way differentiated tissues, even when converted to meristematic activity in a callus, are less readily brought back
to the embryonic state. However, no extensive attempts to produce
embryos in a completely defined nutrient system have been described in
detail ; it may well be that appropriate sequential exposure to the proper
balance of nutrients and known hormones and hormone-like materials
will make it possible to reproduce normal embryogenesis from single
somatic cells derived from callus parenchyma. The technique of embryo
induction in callus tissue dispenses with the need for dissection of imma-
53
1963), from embryos of the orchid Vanda (Rao, 1963), and from callus
tissues derived from cultures of ovaries of the umbelliferous genus
Anethum
(Johri and Sehgal, 1963). Ranga Swamy (1961) also reported
the development of pseudobulbils from callus tissue derived from the
nucellar tissue of a Citrus species. Some interpretation of the origin of
these embryos from such callus tissues is given by Maheshwari and Ranga
Swamy (1963). One striking feature of several of these studies was that
adventive embryo formation seemed to be markedly stimulated by treatment of the embryos in culture with casein hydrolyzate.
Most dramatic have been the reports by Steward et al. (1964) and
Halperin and Wetherell (1964) in the United States and Kato and
Takeuchi (1963) in Japan that callus tissues derived from wild carrot
embryo, root or hypocotyl, cultured on a coconut-milk medium on agar
and then subcultured under different conditions, spontaneously differentiated bipolar embryos which even passed through the developmental
stages typical of ovular embryos of wild carrot. Steward found that
tissues derived from immature embryos placed in culture produced a
friable callus which could be cultivated in liquid coconut-milk medium
as a suspension. Such a cell suspension when plated out on the same
medium in agar plates formed thousands of carrot embryos in such
numbers as to demonstrate without direct examination that many
embryos were, in fact, derived from very small cell clumps and even
single cells. In the study by Halperin and Wetherell (1964), adult wild
carrot root was used to form the initial carrot callus, and from this
callus, cultured on a variety of complex media on agar, there developed
typical bipolar embryos. Recently Halperin (1964) has described some
of the effects of nutrients on embryo development in this system.
At the present time, greatest success in this direction has been
achieved with the wild strain of Daucus carota L.; several other members of the Umbelliferae tested in the same way have not shown the
capacity for embryo formation under these conditions (Halperin and
Wetherell, 1964). The greater tendency of callus derived directly from
embryos to form embryos readily (Maheshwari, 1963a; Steward et al.,
1964) suggests that in some way differentiated tissues, even when converted to meristematic activity in a callus, are less readily brought back
to the embryonic state. However, no extensive attempts to produce
embryos in a completely defined nutrient system have been described in
detail ; it may well be that appropriate sequential exposure to the proper
balance of nutrients and known hormones and hormone-like materials
will make it possible to reproduce normal embryogenesis from single
somatic cells derived from callus parenchyma. The technique of embryo
induction in callus tissue dispenses with the need for dissection of imma-