J Integr Plant Biol. ›› 1963, Vol. 11 ›› Issue (2): -.

• Research Articles •    

Studies on the Structure and the Ontogeny of Laticiferous Canals of Decaisnea fargesii Franch.

Hu Zheng-hai   

Abstract: Decaisnea fargesii Franch. is one of the rubber plants which have received considerable attention in recent years. The rubber of Decaisnea fargesii occurs only in the laticiferous canals of the pericarp and there is neither laticiferous canal, nor rubber substances in its roots, stems and leaves. In the present paper, a preliminary result on the research of the structure and the ontogeny of the laficiferous canals of Decaisnea fargesii is reported. In the pericarp of the mature fruit, an aggregate fleshy follicle, of Decaisnea fargesii, there are numerous white colored laticiferous canals which are easily recognized with the naked eye. These canals connect with each other to form a reticulum. The fundamental structure of the pericarp of the young flowers is not different from that of other flowering plants. However, the protoplasm of the outer epidermal cells of the pericarp is more dense and it takes stains more deeply than that of the cells of its inner side. After the blooming fertilization, numerous spots on the outer epidermis of pericarp become centers of activity. There the cells begin to divide more actively than the other portion. As a result, numerous minute papillae are simultaneously formed. As the cells continuously divide, the papillae are gradually elevated and enlarged. At the bases of these papillae are depressions which become canal-like structures. These connect to form a reticulum below the surface of pericarp. When the canals reach a depth of 200–300μ, the divisions of the epidermal cells flanking the canals gradually slow down, but these cells increase in volume. Because the cells enlarge in anticlinal direction much more than in periclinal direction, the canals become narrower and narrower as the cell enlargement continues. Finally, the lateral walls of the canals meet each other and become fused. Here after enlargement of the epidermal cells are restricted to the lower portion of the canals. The whole structure viewed in cross-section is like a flask. At this stage, the epidermal cells in the lower portion of the flask-like structures are characterized by their larger in volume, larger nucleus, denser-protoplasm and smaller vocuoles. The chloroplasts formerly present disappear and some deeply stained particles appear in the protoplasm. Therefore, the morphology and the structure of these cellgroups are quite different from other epidermal cells of the pericarp including those on the surface and in the upper portion of canals. These groups of cells may be called secretory epidermal cells. At the end of the cells enlargement, the secretory epidermal cells of the lower portion of the canals separate each other and their walls begin to disintegrate. As these activities extend to every part of the secretory epidermal cells, a lysigenous intercellular canal is finally formed. The epidermal cells of the upper portion of the flask-like canals remain intact thus burying the canals formed in the mesocarp of the fruit. The protoplasm and inclusions of the disintegrated cells assume the appearance of milky fluid in the canals. Thus these canals should be regarded as laticiferous canals. During the further development of the pericarp, 2–4 layers of parenchymatous cells of the mesocarp surrounding the disintegrated epidermal cells break off. This makes the diameter of laticiferous canals to be further enlarged. In general, the ontogenetic processes of the laticiferous canals of Decaisnea fargesii include (1) elevation of the external epidermal cells of pericarp, (2) depression of the epidermal cells in the peripheral zone of the papillae, (3) formation and burying of the canals, and (4) disintegration of the secretory epidermal cells. Such a complex phenomena in formation of the laticiferous canals of Decaisnea fargesii is the special type in intercellular canals of plants. Within the pericarp of fully matured fruits, the diameter of the laticiferous canals may reach 600–800μ and their structure resembles the schizogenous intercellular canals generally occurring in other plants in which no special peripheral sheath-like cells has been observed. They remain in the mesocarp, covered externally by 6–9 layers of cells and form a reticulate system parallel with the outer wall of the fruit. According to the present analysis on their structure, ontogeny and distribution, the laticiferous canal system of Decaisnea fargesii is obviously different from the laticiferous tubes and the intercellular canals usually observed in the other plant. Their special type of formation is probably connected with the localization of their occurrence and particularly in relation with the characteristics of development of the fleshy fruit.

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