北美鹅掌楸混合芽的发生和分化

北美鹅掌楸(Liriodendron tulipifera L.)的混合芽通常位于短枝的顶端,从发生到开花历时3年,混合芽的营养端向花端的转化发生在第二年的6月。绒毡层为分泌型,四分体的形成为同时型,排列方式以十字交叉型和四方型为主,撒粉前夕为单细胞花粉。离心皮雌蕊,多数,螺旋状排列,子房和胚珠同时发育,每个子房有2个悬垂的倒生胚珠。蓼型胚囊,开花时大多为二核期。花期持续时间长达20多天,雌雄蕊异熟,柱头可授期短,仅1～2天。最后讨论了混合芽分化与结籽率低的关系。

INITIATION AND DIFFERENTIATION OF MIXED BUD IN LIRIODENDRON TULIPIFERA L.

(1) Usually, the mixed bud of Liriodendron tulipifera L. is in the apex of short shoot. The mixed bud took three years to develop into anthesis from initiation. The transition from a vegetative to a floral apex occurs in June of the next year. (2) The taptum is of the gladular type. The formation of tetrad is of the simultaneous type. The mostly tetrad follows the tetrahedron type and the decussate type. Just before shedding pollens are singe grains with one-cell. (3) The apocrapy pistil are many. The ovary and ovule develop simultaneously. Each ovary has two podulous anatropous. It is the poly-gonum-type enbryo sac and usually in the nucleared periods when it blooms. (4) This period of anthesis can last as long as twenty days. The mature of pistil and stamen is unsynchronous. The receptive stage of stigma is as short as two days. (5) The relationship of the mixed bud's differentiation and the low seeding rate is discussed in this paper.