Abstract:

Except for Pseudolarix, which is endemic to China, the late embryogeny of ten

genera of Pinaceae has been reported before in the diffferent degree.  Among them the mature

embryos of Keteleeria evelyniana are different from those of the others in having well-developed

cotyledons and a very short hypocotyl.  As far as information we have is concerned there are

three types in structure of the mature embryos of Pinaceae.  The first type occurs in Keteleeria

and Cedrus, which have very well-developed cotyledons; the second one appears in Picea and

Larix, in which the hypocotyl and the root cap are equal in length; the third one, to which

Pinus bungeana belongs, includes all the other genera of Pinaceae.  The last type is of a promi-

nent hypocotyl in the mature embryos.  It is interesting to note that the mature embryos of Tor-

reya grandis and Keteleeria evelyniana are very similar in having specially developed cotyle-

dons, while the proportions of the various tissues in the mature embryo in Fokienia of Cupres-

saceae as well as Taxus and Amentotaxus of Taxaceae are similar to those of Pinus bungeana.

The pith and secretory cells are usually present in the mature embryos of Pinaceae.  Although

no pith is present in those of Metasequoia and Taiwania of Taxodiaceae, the secretory cells ge-

nerally occur in their embryos in Fokienia of Cupressaceae and Taxus and Pseudotaxus of Ta-

xaceae, neither pith nor secretory cells are present in their hypocotyl.  From above, the struc-

tures of mature embryos among Pinaceae, Taxodiaceae and Cupressaceae are different from one

another to some degree.

      The most outstanding feature of the matur  embryos in Pinus bungeana is that the shoot

apex is very well developed, with a high H/D ratio, about 0.83 on an average, even up to 0.96

in some case. Above-mentioned H/D ratio of Pinus bungeana is rare in the mature embryos of

conifers.  Gifford (1943) reports that the average H/D ratio of shoot apex of Ephedra altissima

is from 0.44 to 0.68, while in 5-year-old branch apex of Pinus ponderosa, the average ratio is

about 0.25, and that in l5-year-old branch apex is about 0.35.  For the apex of the dormant

short shoots of Pinus densiflora the average ratio is about 0.35, but that of shoot apex is about

0.52 when new buds have just formed.  According to the present data about shoot apices of both

branches and mature embryos, the average ratio of shoot apex of mature embryos in Pinus bun-

geana is the largest one.  From the present investigation the shoot apex of mature embryos of

Pinus bungeana exhibits four distinct tissue zones, i.e. the apical initials, the central mother cell

zone, the peripheral tissue zone and the rib meristem.  It is worthy of note that the shoot apex

of Pinus strobus may be divided into five zones, including transition zone between central mother

cells and rib meristem (Owston, 1968).   Four zones are recognized in the shoot apex of

Pinus lambertiana and P. ponderosa, without transition one (Sacher, 1954).  From cytological

zonation, the shoot apex of mature embryos in Pinus bungeana is rather similar to that of Pinus

lambertiana and P. ponderosa.

Key words: Pinus bungeana, late embryo, shoot apex