Fig. 4. A pollen mass, more highly magnified, separated from its gland and arm, and divided
transversely, to show its cellular structure (first discovered in Asclepias curassavica in
1805 by Mr. Bauer), with grains of pollen,- their granules, and some drops of an oily fluid.
5. A pollen mass entire, with a small portion of the arm adhering to its apex. Magnified
as fig. 4.
6. A transverse section of a pollen mass, still more highly magnified, in one of the cells of
which is seen the single grain (or inner membrane), also separately exhibited to show
that it is simple and slightly angular.
7. The pistillum with pollen masses, that have burst and protruded their tubes, applied to the
base of the stigma, the glands and their arms being removed. The cords formed by the
pollen tubes have passed along the corresponding sides of the conical base of the stigma,
and have reached the tops of the styles.
8. A longitudinal section (more highly magnified) of the conical base of the stigma with the
two styles, to show more distinctly the course of the pollen tubes.
9. A pollen mass after bursting, with its cord formed of the pollen tubes, entering the apex of
the style, which is there lacerated.
10. The two ovaria with their styles, one being somewhat enlarged in consequence of impregnation,
and opened longitudinally; exhibiting pollen tubes extending from the apex of the
style to the commencement of the placenta.
1 1 . The same two ovaria and styles, both opened, to show that in one (the left), which is somewhat
smaller, no pollen tubes are contained; th e other (the right), which is impregnated,
| shows the tubes reaching the ovula, but not extending further, j
12. Two grains of pollen (or rather grains deprived of their outer membranes), with portions of
their tubes and contained spheroidal granules; proving that the tubes are extensions of
this (the inner) membrane. Very highly magnified.
P late XXXI.
Asclepias phytolaccoides.
Fig. 1. An expanded flower (magnified), from which two of the foliola coronse and one anthera
been removed.
2. The complete pistillum, and on one side two of the antherae, the membrane formed by the
united filaments being cut off a little below the stigma; on the other side, a naked pollen
mass applied to the stigma, with its gland and arm adhering.
3. A longitudinal section of fig. 2, to show on the left side a pollen mass, with a small portion
only of the arm adhering, applied to the base of the stigma, and which, having burst, shows
the protrusion of the cord formed by the pollen tubes.
4. A longitudinal section of one half of the stigma and the corresponding style transversely cut
near the base, showing more distinctly the position of the pollen mass with the protrusion
and course of the tubes.
5. The style of fig. 4 laid open lengthways, exhibiting within its cavity and beyond it the
pollen tubes reaching the apex of the placenta, a reflected portion of which, with three
of its ovula, is also shown.
Fig. G. An impregnated pistillum, of which the style is laid open longitudinally, and the
placenta, thickly covered with ovula, exposed, to show the descent and course of the pollen
tubes.
7. A pollen mass, to the apex of which the base of the arm adheres, with pollen tubes protruding
from the point of dehiscence. More highly magnified.
8. A transverse section of a pollen mass, showing an arrangement of the cells somewhat
different from that of A. purpurascens, there being here amiddle irregular series, the cells
of which in some cases appear to separate and cover the grains after the production of
the tubes.
9. Two grains of pollen with portions of their tubes, very highly magnified, the grain to the
left having its outer covering or membrane, which is removed from the grain to the right,
and shown separately further to the left.
10. A pollen mass which has burst and protruded its tubes, exhibited as entering the cavity of
the style, which is laid open to show the commencement of their descent.
11. Two pollen masses (with their arms and gland), which have burst and protruded their
tubes while still inclosed in the cells of the antherm; this happening in A. phytolaccoides
in that particular kind of decay mentioned in p. 529 of the text.
PLATE XXXII.
Fig. 1. Two pollen masses of Asclepias purpurascens with protruded tubes; the only instance
met with in which both cords are introduced into the same style.
2. A grain of pollen, of the same species, with a portion of its tube; the unusual form
probably caused by the pressure of other grains and their tubes.
3. A grain of pollen of Asclepias purpurascens containing numerous minute granules and
two larger drops or globules of an oily fluid.
4. 5, and 6. Various combinations of pollen masses of Asclepias purpurascens. In these it is
supposed that the insect having removed and applied to the stigma some of the masses,
has extracted, by means of the arms still adhering to it, other masses with their glands
and arms.
A combination of the same kind, different from and more remarkable than any of these,
but perhaps not very accurately represented, is given, in his * Microscop. Entdeck./ tab.
xxxvi, fig. 8, by Gleichen, who appears (op. cit., p. 81) to have also met with other
combinations, without suspecting in any case the real cause of such apparently anomalous
structures.
7. A flower-bud of Asclepias curassavica in the earliest stage in which I was able to
distinguish its parts ; the unopened corolla in its place with one of the sepala, the other
four being exhibited separately. Highly magnified.
8. The corolla of fig. 7 opened and in part removed, to show the state of the contained organs.-
the figure exhibiting two petals hardly cohering at base; within these, two distinct petallike
bodies, alternating with them, and which are the antheræ ; and two other smaller
bodies, which are the pistilla as yet unconnected.