(4) The establishment of cultures consisting entirely of preglobular stage proembryos (PGSPs) is a slow process.
(5) Establishment of PGSPs can be hastened by repeated mashing or wounding of the first-formed globular stage embryos at the time transfers are made.
(6) The growth rate of PGSPs maintained at pH 4 can be nearly doubled by the addition of a synthetic auxin (i.e., 4.5 [[micro]molar] 2, 4-D).
(7) Transfer of cultures consisting of "undifferentiated" callus and PGSPs - initiated and maintained in medium at pH 5.7 with the synthetic auxin 2,4-D - to hormone-free medium at pH 4 results in continued multiplication of PGSPs but not "undifferentiated" callus.
(8) PGSPs cannot be maintained as such if the medium pH is maintained at or above 4.5.
(10) Continued development of PGSPs requires a source of reduced nitrogen in the medium.
It is not understood why low external pH allows embryogenic carrot cells (PGSPs) to multiply without development into later embryo stages on hormone-free medium.
At pH values below 4.5, PGSPs did not organize into later-stage embryos, and this was interpreted as a poor response.