. The classification of flowering plants. Fig. 23. Juniperus thurifcra, a heteromorphic species shewing concrescentsquamiform leaves in decussate pairs characteristic of the adult shoots;on younf, plants and vigorous shoots of older ones the leaves are acicularand in whorls of three as in J. drupacea. From Veitch. Ill] CONIFERAE 85 communicating by pits with the sieve-tubes, and known asalbuminous cells. They probably correspond functionally withthe companion-cells of Angiosperms. The tracheides formed towards the end of each season aremuch narrower and have much thicker walls than those forme
. The classification of flowering plants. Fig. 23. Juniperus thurifcra, a heteromorphic species shewing concrescentsquamiform leaves in decussate pairs characteristic of the adult shoots;on younf, plants and vigorous shoots of older ones the leaves are acicularand in whorls of three as in J. drupacea. From Veitch. Ill] CONIFERAE 85 communicating by pits with the sieve-tubes, and known asalbuminous cells. They probably correspond functionally withthe companion-cells of Angiosperms. The tracheides formed towards the end of each season aremuch narrower and have much thicker walls than those formedin the spring ; this contrast between spring and autumn woodcauses the characteristic demarcation of annual rings. Schizo-genously formed resin-passages are common in the cortex, andoccur also in the primary and secondary wood, and sometimesin the larger medullary rays as in Pinus or in the phloem as Fig. 24. Transverse section of leaf of Tsuga Brunoniana x 30, shewingthickened epidermis, hypoderma confined to the lateral margin, palisadearrangement of upper mesophyll, a single vascular bundle (/) and amedian resin-canal (r). From Veitch. The anatomy of the leaf shows marked xerophytic epidermal cells are thick-walled and strongly cuticularised,and each stoma is sunk at the bottom of a pit. Below the epi-dermis are thick-walled, strengthening bands of mesophyll in the broader leaves is differentiated into
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectbotany, bookyear1904
