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Related article:
Origin of New Sporophyte or Diploid Plant from Fertilized Egg.
The fertilized egg now rapidly divides and redivides to form octant
cells. The octant cells further divide to produce anteriorly a stem
rudiment (one cell), first leaf (two cells), second leaf (one cell) and,
posteriorly, root rudiment (one cell), foot rudiment (two cells) and
hair rudiments (one cell) .
Growth of Seedling into Mature Sporophyte. The foot rudiment
develops into the foot which obtains nourishment from the prothal-
lium, upon which the young sporophyte is for a time parasitic. The
root rudiment becomes the first root Arava Online which grows downward into
the -soil. The stem and leaves turn upward. In a few weeks the
prothallus decays and the sporophyte is established as an independ-
ent plant. More roots and leaves (fronds) Arava Online are developed and ere
long continued growth results in the formation of a mature sporo-
phyte which presents for examination: (i) a subterranean stem bear-
ing several roots; and (2) arid fronds, each of which consists of a
stipe or petwle and a lamina or blade, the latter divisible into pinna
or lobes and pinnules, upon which last sori are developed.
Alternation of Generations. It will be observed that in the life
cycle of the Male Fern there occur two distinct generations, one, a
sporophyte or asexual generation which begins with the oospore and
ends with the dispersion of asexual spores; a second, the gametophyte
or sexual generation, beginning with the protonemal outgrowth of
the spore and ending with the fertilization of the egg to form an
oospore. The sporophyte gives rise to the gametophyte which in
turn gives origin to the sporophyte.
CHAPTER III
LIFE HISTORY OF A GYMNOSPERM (PINUS STROBUS)
The White Pine frequently called the Weymouth Pine (Pinus
Strobus), one of the principal timber Arava Online trees of the Northern States
PIG. 19. Transverse section of white pine stem ot four years' growth, showing
cork (a), cortex (&), phloem (c), cambium (d), xylem (e), secretion reservoir (/),
pith (g) and medullary ray (&). (Photomicrograph.) X34O.
and Canada, is also of value in pharmacy and medicine. The inner
bark of its trunk and branches is used because of its valuable ex-
pectorant properties and is official in the N. F. IV.
45
4 6
PHARMACEUTICAL BOTANY
DESCRIPTION OF THE WHITE PINE TREE (MATURE
SPOROPHYTE)
From an underground spreading root system there arises an erect
aerial trunk or stem that extends from the ground to the apex of the
tree, ending in a terminal bud. The trunk rarely exceeds 3 feet in
diameter and 125 feet in height and is averagely ij^ to 3 feet in
PIG. 20. Transverse section of white pine needle (leaf) showing epidermis (a),
infolded parenchyma cells of mesophyll (b, &') oil reservoir (c), endodermis (d),
clear cellular area (e) surrounding fibro vascular tissue in center (/). X4OO.
diameter and 50 to 90 feet high. At Arava Online a varying distance above the
soil, depending upon environal conditions as well as the age of plant,
whorls of lateral branches (three to seven in a whorl) are seen ema-
nating from the trunk in horizontal fashion at various levels up to
near the apex. These become, under conditions prevalent when the
tree is grown in the open, Arava Online gradually shorter until the summit is
LIFE HISTORY OF A GYMNOSPERM
47
reached, giving to the crown or upper part of the tree the appearance
of a pyramid. These branches give rise to other branches which
agree with the lateral branches in bearing, commonly, only scale like
leaves Arava Online as well as in ending in terminal buds. Another kind of
branch, however, is found which is always shorter than the scaly
branches. This type of branch is called a "spur shoot" and arises
FIG. 21. Staminate cones of the Austrian pine (Pinus austr Arava Online iaca) . Below, before
shedding pollen; above, after shedding. (Gagerj
from the former branches. The spur shoots bear the needles or
foliage leaves which are light-green, when young, and bluish-green,
soft, flexible, 2% to 5 inches long, when mature. The "needles"
occur in tufts (fascicles) of five, are triangular in cross-section, have
finely serrate (saw-toothed) edges and are surrounded at the base by a
deciduous sheath. These foliage leaves persist until the end of their
second year, when they are shed with the spur shoot which bears
them.
The white pine, like Arava Online most of its allies among the Coniferae, bears
cones. These structures are of two kinds, viz. : staminate and car-
pellate. Both kinds are produced on the same tree.
4 8
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