. A textbook of botany for colleges and universities ... Botany. Fig. 772. — A longitudiaal section through a portion of the stem of .5o/«:orttMi, showing oblique palisades (^), and also a "storage" tracheid (t); the arrow is directed toward the stem apex; jf, stoma; considerably magnified. to the leaf surface, regardless of the position of the leaf in relation to light. The position of the palisade layers seems relatively fixed in most cases (not in Lactuca and in Eucalyptus), a rudimentary palisade region often being discernible in the bud; in sub- sequent development the thickness
. A textbook of botany for colleges and universities ... Botany. Fig. 772. — A longitudiaal section through a portion of the stem of .5o/«:orttMi, showing oblique palisades (^), and also a "storage" tracheid (t); the arrow is directed toward the stem apex; jf, stoma; considerably magnified. to the leaf surface, regardless of the position of the leaf in relation to light. The position of the palisade layers seems relatively fixed in most cases (not in Lactuca and in Eucalyptus), a rudimentary palisade region often being discernible in the bud; in sub- sequent development the thickness of the layer, but not its position, may vary as external conditions vary. Thus light appears to affect chiefly the cell length, the region of develop- ment and the orientation of the pali- sade cells being due to other and mostly unknown causes. The influence of light upon cell elongation might be conceived of as direct or indirect. In many but not in all albescent leaves the palisades stop sharply at the edge of the green tissue (fig. 773), although the green and colorless spots are ex- posed equally to the light; thus palisade de- velopment appears to be correlated with the formation or with the activity of chlorophyll rather than with light directly. Again, the palisade length in- creases and decreases with the amount of car- bon dioxid, seeming to indicate that palisade size is associated with synthetic activity. Palisades and trans- piration.—Not all cases of palisade development can be referred to light,. Fig. 773. — A cross section of an albescent leaf of Abutilon; to the right of the vein (v) is a chlorophyll- bearing region with two rows of palisade cells (p) and about three layers of sponge tissue (/); to the left is a colorless portion entirely without palisade cells, this part of the leaf having remained in its original undifferentiated state; the lower epidermis (e) contains chlorophyll, even in the albescent region of the leaf; note the lack of symmetry, d
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectbotany, bookyear1910
