. Physiological botany; I. Outlines of the histology of phænogamous plants. II. Vegetable physiology. Plant physiology; Plant anatomy. SECONDARY STEUCTUEE. 135 Secondary Structure. 386. It has been noticed that the flbro-vascular bundles of monocotyledons differ from those of dicot3ledons chiefl}- in the possession by the latter of a layer of mcrismatic tissue (cambium) between the cribrose and woody portions. The stems of peren- nial dicotyledons increase in thickness from yeav to j'ear chiefly bj' the annual production of a new mass of wood upon the in- side of this layer, and of liber upon
. Physiological botany; I. Outlines of the histology of phænogamous plants. II. Vegetable physiology. Plant physiology; Plant anatomy. SECONDARY STEUCTUEE. 135 Secondary Structure. 386. It has been noticed that the flbro-vascular bundles of monocotyledons differ from those of dicot3ledons chiefl}- in the possession by the latter of a layer of mcrismatic tissue (cambium) between the cribrose and woody portions. The stems of peren- nial dicotyledons increase in thickness from yeav to j'ear chiefly bj' the annual production of a new mass of wood upon the in- side of this layer, and of liber upon the outside ; but the stems of most monocotyledons have no provision for annual increase in diameter. Hence it is convenient, in spite of numerous anomalies, to consider the secondary struc- ture of the stem under these two heads. 387. Secondary structure of monocotyledonous stems. As has been alread3' observed, the pri- mary bundles in palms run from the leaves in curves of long ra- dius until they again approach the surface of the stem, and their fullest development is found in the middle part of their course. While a cross-section exhibits these bundles as scattered without much order in a mass of paren- chj'ma, a vertical section shows that they entered the stem m at diflJ'erent heights (since the leaves with which they were developed were at different points on the stem). A vertical section can displaj- only parts of most of these curved bundles. At the stem of a palm just below the crown of leaves there are as many bundles seen in a cross-sec-. IP oth Type. A central mass of secondary tissue, formed from eentnil meris- tem. Intermediate zone well developed; c. g., Triglochin maritimum. 6tli Type. Bundles having several distinct lilier elements; e. g., Tamus communis. (Anatomic de la tige des Monocotyledones, Ann. des Sc. nat., ser. 6, tome v., 1878, p. 1.) Fig. 111. A diamond-shaped mesh of primary fascicles intermingled with secondary fascicles in the stem of an O
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