The induction, development, and heritability of fasciations . mechanical stratum, which for conveniencewill be termed the median band of chlorenchyma. In the younger stems themedian band is practically continuous, but in the older ones it becomesbroken up into distinct masses. From the median band there passes inward,like the spokes of a wheel, the medullary rays of the inner part of the rays in the younger branches are well supplied with chlorophyll. Turning now to the woody cyHnder, we find that the medullary rays, aportion of the wood parenchyma, and the pith are chlorophyll-be
The induction, development, and heritability of fasciations . mechanical stratum, which for conveniencewill be termed the median band of chlorenchyma. In the younger stems themedian band is practically continuous, but in the older ones it becomesbroken up into distinct masses. From the median band there passes inward,like the spokes of a wheel, the medullary rays of the inner part of the rays in the younger branches are well supplied with chlorophyll. Turning now to the woody cyHnder, we find that the medullary rays, aportion of the wood parenchyma, and the pith are chlorophyll-bearing. Inbranches 1 cm; in diameter the entire medullary ray from cortex to the pithis so well provided with chlorophyll that the cut end of the branch undera hand-lens appears grass green. In much larger stems, however, and insmaller ones from a less healthy plant no chlorophyll, or scarcely any, is to Fig. II.—Parkitisonia torreyana: Segmentof stem 7 mm. in diameter, to show thedistribution of chlorophyll. Lettered as inpreceding figures. Cannon Plate 4. PARKINSONIA MICROPHYLLA. The species from which this branch was takendeciduous ; the branches are green and function as leaves. April 25, I 907. PARKINSONIA. 25 be found in the wood. The wood parenchyma in the immediate vicinityof the ducts may contain chlorophyll (fig-. 10). As to chlorophyll in the pith, it need only be said that it occurs sparinglyin stems 1 cm. in diameter and is not present in the older and larger branches. The chlorophyll disappears from the stem in a very regular leaves the epidermis first, then the pith, then the inner medullary rays;after this the wood parenchyma, then the medullary rays of the cortex andthe median band, and finally, when cork is formed, the outer band. Thatis, with two exceptions, the chlorophyll disappears from the stem in a cen-trifugal direction. The exceptions were most marked in stem of P. torreyana8 mm, in diameter, in which practically all of the chlorophyll of
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