CONDALIA SPATHULACA. 



11 



The chlorophyll band is a relatively naiTow tissue which lies rather deeph^ 

 in young: stems, but in older ones much nearer the surface (see table 

 of measurements below) . The cells are either cuboid or slig-htly elon^-ated. 

 If the latter the long- axis is tangential to the surface. 



AVith increase in diameter certain changes take place in the stem which 

 are most marked in the cortex. Cork is formed in very small stems. In 

 a stem 2 mm. in diameter and 5 cm. from the tip it was observed in the 

 hypodermal cells, where a considerable amount of periderm was organized. 

 This is more pronounced in branches 4 mm. and still more in those 7.5 mm. 

 in diameter. The phelloderm, however, is not formed until the stem is 

 somewhat older. In a stem 1.2 cm. in diameter the phelloderm was about 

 two cells in thickness and was chlorophyll-bearing; in a branch 1.7 cm. in 

 diameter the amount of chlorophyll-bearing- phelloderm was so great as to 

 considerably increase the width of the chlorophyll tissues. The chlorophyll 

 early leaves the wood and the pith; in a stem only 7.5 mm. in diameter it 

 was confined to the outer portion of the cortex. 



The following measurements were made: 



COVILLEA TRIDENTATA. (Plate I, B, and fig. 5. 



The plant from which the branch stitdied was taken is growing near the 

 road a few meters east of the Laboratory building. Sections were cut at 

 the following distances from the tip: 5, 10, 20, 35, 65, 95 cm., and were 

 1, 1.5, 3, 4.5, 7.5, 9.5 mm., respectively, in diameter. 



The young and angular stem, 1 mm. in diameter, has the following gen- 

 eral relations of its tissues: Within the epidermis, which has a rather thin 

 cuticle, lies the broad chlorophyll band, which is about three cells in thick- 

 ness. A discontinuous hard-bast ring- is placed immediately within the 

 chlorophyll band. This is made up of larger and of smaller groups, of which 

 the former lies opposite the angles of the stem. More or less stony tissue 

 also is found in the same ring. Between the groups of mechanical tissue 

 is thin- walled parenchyma. Within the hard-bast ring, and separating it 

 from the cambium, are the distal ends of the medullary rays and paren- 

 chyma between them. There is nothing noteworthy in the present connec- 

 tion regarding either pith or wood. 



