芭樂樹幼枝形成層活動之季節性

Abstract

1．芭樂樹周皮在二年生的幼枝裹已取代表層組織的功能，木栓形成層向外分裂產生的木栓組織只含有一種形態的木栓細胞，木栓形成層的?命極長，至少在五年之中未失去其活動力，栓皮組織不如木栓組織發達，有些細胞內含有結晶體。 2．皮層由等徑的薄壁細胞和不規則形的石細胞構成。薄壁細胞含有葉綠體，或?多面體結晶所佔據，細胞常連接成串。石細胞具極厚之次生細胞壁，其上有無緣孔，射線延長線上的擴張組織隨形成層的發育逐漸發達，七月至九月最?顯著。 3．管束形成層之活動期極長，自二月初至十一月，六月初?其活動之最高潮時期，其活動速率受氣溫影響十分顯著，溫度逐漸上升時，形成層活動力增強，28℃左右時活動最旺盛，超過此溫度後，並不能再促進其活力，反而有減慢的現象。形成層帶細胞的層數隨其活動速率的快慢有所增減。 4．後生木質部?典型的散孔材，導管細胞口徑?20至50μ之間，第一年的木材裹就有?充細胞出現；射線密集，單層和多層（兩層居多）射線俱存；?向薄壁細胞?離管型分佈，自散狀至帶狀。 5．韌皮部組織不若木質部發達，除節管細胞及伴細胞外，韌皮薄壁細胞因含有多面形結晶十分顯眼。不規則形的石細胞單獨存在或成帶分佈，細胞形態與皮層內者無異。 6．髓部亦由薄壁細胞及不規則形之石細胞所組成，此處之薄壁細胞內無葉綠體，而?多面體或晶簇狀結晶所充斥，石細胞與皮層，韌皮部內者相同。 7．芭樂樹的葉芽於四月初大量萌發，七月以後新葉生長逐漸停止；開花期則於五月和十月時較?集中，其餘時期亦斷續有開花現象。形成層之活動期開始於葉芽萌發之前，第一次花期正?形成層活動旺盛之時，第二次的花期則在形成層活動的末期。

1. The primary epidermal tissue was replaced by periderm when the young branch of guava tree (Psidium guajava Linn.) bore two to three growth rings. The phellogen, cork cambium, produced less phelloderm cells than the phellem which was composed of only one type of cells. The second layer of new cork cambium has not been identified in all the branches which bore one to five growth rings during the period of this experiment. Some of the cells in phelloderm contain prismatic crystals. 2. Cortex is made up of two kinds of cells: isodiametric parenchyma and irregular stone cells. Chloroplasts are constantly present in the parenchyma. Occasionally some parenchyma cells are occupied by prismatic crystals and they are always arranged in a string. The expansion tissue in the cortex developed as the vascular cambium began to activate and they were in the grand period of active stage during July to September. 3. The period of cambial activity was very long. It began in early February, ended in November. The most conspicuous cambial activity was seen in early June. When the temperature gradually rised the cambial activity increased. But it slowed down as the temperature was over 28℃. 4. A typical diffuse-porous wood is showed in the secondary xylem. Tyloses are observed even in the wood formed in the first year. Both uniseriate and multiseriate rays are close distributed. Apotracheal axial parenchyma appear in either diffuse or banded form in three to five rows. 5. Pith is also composed of parenchyma and brachysclereids (irregular stone cells). Chloroplasts are not found in the parenchyma cells but the various shapes of crystals: prismatic, druses and irregular forms are abundant in them. 6. At the beginning of April the leaf buds sprouted in a large amount. Then, the new leaves continued to grow till late July. Two main flowering periods were figured as in May and October. The reactivation of the cambium began prior to the sprouting of the leaf buds and the first flowering period was corresponded with the grand active stage of the cambium.