Characteristics of the phloem and the cortex

Two groups can be distinguished:

a) The phloem and the cortex of Apollonias (Fig. 16) and Laurus (Fig. 17) have simple structures. Sieve-tube elements and parenchyma cells are difficult to differentiate in transverse sections. Ray dilatations are characteristic. The presence of crystal sand in ray cells is unique to Laurus azorica.

b) Collapsed sieve-tube elements (Figs. 18 and 20) occur in both Persea species. Laticifers occur in Persea indica (Fig. 19). Intercellular ducts are surrounded by an epithelium in the phloem, the cortex (Fig. 20) and the pith (Fig. 21) of Persea americana. Irregular groups of sclereids are present in Persea americana (Fig. 20).

Fig. 17. Simple construction of the phloem. Sieve-tube elements and parenchyma cells are difficult to differentiate. Phloem of a 4 m-high tree, Laurus forest, subtropical climate, Gomera, Canary Islands. Laurus azorica, transverse section.

Fig. 16. Simple construction of the phloem. Sieve-tube elements and parenchyma cells cannot be differentiated. Phloem of a 4 m-high tree, Laurus forest, subtropical climate, Gomera, Canary Islands. Apollonias barbujana, transverse section.

Fig. 17. Simple construction of the phloem. Sieve-tube elements and parenchyma cells are difficult to differentiate. Phloem of a 4 m-high tree, Laurus forest, subtropical climate, Gomera, Canary Islands. Laurus azorica, transverse section.

Fig. 18. Phloem with irregular lines of compressed sieve-tube elements. Phloem of a 4 m-high tree, Laurus forest, subtropical climate, Gomera, Canary Islands. Persea indica, transverse section.

Fig. 19. Cortex with laticifers. Bark from a twig of a 4 m-high tree, Laurus forest, subtropical climate, Gomera, Canary Islands.

Persea indica, transverse section.

Fig. 19. Cortex with laticifers. Bark from a twig of a 4 m-high tree, Laurus forest, subtropical climate, Gomera, Canary Islands.

Persea indica, transverse section.

Fig. 20. Phloem with irregular groups of sclerenchyma cells and axial canals surrounded by epithelial cells. Phloem of a 4 m-high tree, Laurus forest, subtropical climate, Gomera, Canary Islands. Persea americana, transverse section.

pith

Fig. 21. Pith with axial canals surrounded by epithelial cells. Pith from a twig of a 4 m-high tree, Laurus forest, subtropical climate, Gomera, Canary Islands. Persea americana, transverse section.

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