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 prominent hypocotyl in the mature embryos. It is interesting to note that the mature embryos of Torreya grandis and Keteleeria evelyniana are very similar in having specially developed cotyledons, while the proportions of the various tissues in the mature embryo in Fokienia of Cupressaceae 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 generally occur in their embryos in Fokienia of Cupressaceae and Taxus and Pseudotaxus of Taxaceae, neither pith nor secretory cells are present in their hypocotyl. From above, the structures 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 bungeana 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 Pinuslambertiana and P. ponderosa.

Key words: Pinus bungeana, late embryo, shoot apex