从胚胎发育看穗花杉属的系统位置

穗花杉 Amentotaxus argotaenia 胚胎发育的主要特点是：  原胚在16核时形成细胞壁， 幼胚发育缓慢，并要经过一个冬季低温阶段，一直到第二年种子脱落时，它们还处于简单多胚  的选择时期, 后期胚的发育是在种子脱离母树后进行的。根据胚胎发育特点，穗花杉属在红豆杉科中的系统位置(由原始到进化的顺序)是：穗花杉属，澳洲红豆杉属，红豆杉属，白豆杉属，榧树属。

On the Systematic Position of Amentotaxus from Its Embryological Investigation

The present paper deals with the embryological study and the systematicposition of Amentotaxus argotaenia (Hance) Pilger.  The material used was collectedduring 1980-1981 from Jin-fo Shan,  1400-1600 m,  Sichuan Province,  China.   Thespecies is dioecious.  The male cone sheds its pollen during the period from the end ofMay to the middle of June.  The pollen at mature stage is 2-celled.  Pollen chamberappears obvious at the end of the nucellus.  When pollen grains are dispersed,  megas-pore mother cell,  which is situated deep in the nucellus,  is in meiosis. The megasporedivides mitotically after pollination and the free nuclei of female gametophyte dividefor the last time at the end of June. The wall formation takes place at the stage of 256free nuclei.  The development of archegonia takes place at the beginning of July andthe fertilization occurs about July 20-23.  The fertilized egg  divides  successivelyfour times and results in a 16-nucleate proembryo. The young embryo is developing inAugust.  It is interesting to note that the development of the young embryo is veryslow.  When the seed reaches the mature stage from June to July in the followingyear,  the multicellular masses of the young embryos resulted from simple polyembryonyremain immature within the female gametophyte.  No cleavage polyembryony has beenfound.  The subsequent embryogeny takes place after the seed has shed.     Keng (1975) considers that Amentotaxus links the Taxaceae with Cephalotaxaceae.Our embryological data support Keng’s conclusion since they share  (1)  compoundmicrostrobilus,  (2) 2-celled pollen grains at shedding stage and (3) the rather longlife cycle.  Keng (1975) also mentions that Podocarpaceae may connect with Taxaceaethrough Phyllocladus.  According to Keng the Podocarpaceae is related to Taxaceae tocertain degree.  It is obvious that the primitive spike-like male strobilus like the onein Cordaitales is obviously retained in Podocarpus spicatus and P. andinus of Podocar-paceae and Amentotaxus of Taxaceae.  In addition,  like in Amentotaxus there are 16nuclei before wall formation in the proembryo of Podocarpus nivalis.  These facts maywell indicate that at least the Podocarpaceae and the Taxaceae were derived from a common stock.  As far as the Taxaceae is concerned the authors tend to support theview of Koidzumi (1932) that Amentotaxus and Austrotaxus should be put in the sametribe since both possess the spike-like strobilus,  the long life cycle and the seed matura-tion in the following year. They are probably rather primitive genera in the Taxaceae.The proembryogeny of Torreya is more or less specialized.  It may be placed in a ra-ther advanced tribe and the tribe Taxeae (including Taxus and Pseudotaxus)may bebetween the above two tribes.  In conclusion,  the Taxaceae is related to the Coniferalesin certain respects and,  as Keng (1975),  Harri (1976) and Wang et al. (1979) havepointed out recently,  placing of the Taxaceae in Coniferales is rather justifiable.