With Plate I.
In 1882 Professor Todd published his interesting observations[D] on the
pollination of _Solanum rostratum_ and _Cassia chamæcrista_. Since that
time, so far as the writers are aware, nothing has appeared upon this
subject. During the months of August and September, 1901, opportunity
was afforded the writers for making more extended observations on these
species. The notes here given are the result of these observations.
In some respects, these observations, or the conclusions drawn from
them, differ essentially from those made by Professor Todd; in others
they are practically the same. The writers feel that, even where
observations or conclusions are the same, the confirmation of Professor
Todd’s results is of value, since the data have been collected in a
different locality and a different year.
It must be borne in mind that the lack of agreement between the
observations in the present paper with those made by Professor Todd
is probably largely due to the inferior quality of his material. _S.
rostratum_ had been but recently introduced into southern Iowa when
Professor Todd’s article was written. It apparently did not thrive very
well, the greatest number of flowers mentioned as appearing on any one
plant being ten—a very small number to be produced by a plant of any
considerable size. While also an introduced plant in eastern Kansas, it
has been long and well established, and grows luxuriantly.[E]
The data upon which the conclusions here given are based have been
given largely in tabulated form. For the present purpose, it might have
been sufficient to give only the summarized results of some of the
tables. They have, however, been inserted in full, since the writers
hope that they may be useful in future work on these plants, and since
they believe that the collection of carefully prepared statistical
data of this kind is very valuable for the decision of some biological
questions.
The writers wish to express their gratitude to W.C. Stevens, professor
of botany, for suggestions on the work, and to Hugo Kahl, entomologist
of the University of Kansas, for the identification of the insects. The
drawings were made by Miss Marguerite E. Wise.
_S. rostratum_ is a low, spreading, bushy annual, sometimes attaining a
diameter of four or five feet and a height of one and one-half feet.[F]
The pinnately lobed leaves, as well as other parts of the plant, are
beset with strong prickles. It seems to be especially adapted to arid
regions, thriving on the dry plains of the Southwest.[G]
The material studied by the writers grew, for the most part, in clayey
soil, around old stone-quarries on Mount Oread, a projection of the Kaw
river bluffs. A brief examination was made of material growing in waste
places in St. Joseph, Mo.
During the very severe drought, which extended up to August, _S.
rostratum_ was one of the few plants which were apparently uninjured
and blossomed with any considerable vigor. The most of the observations
were made after the drought was broken by the rain of August 9, when
the plants were in the height of their flowering season.
The flower has a somewhat irregular, wheel-shaped, gamopetalous
corolla, bright yellow in color. Four of the stamens are normal in
their structure, but the fifth, which is on the lower side of the
flower, has attained a length almost twice that of the others. Its
anther is large and tapering. At about the middle it is crooked a
little toward the outside, and its slender, tapering apex is curved
upward. The filaments of all the stamens are very short, bringing the
anthers close up to the base of the corolla. The small anthers are of
about the same color as the corolla, varying sometimes to a greenish
yellow. The large anther, however, is quite different; the proximal
half being of a greenish yellow, while the distal half has a more or
less pronounced purple color. Professor Todd, in his paper, does not
speak of the color of the anthers, but Fritz Mueller,[H] in writing of
_S. rostratum_, says: “All the anthers, as I am informed by Professor
Todd, are of the same dull yellow color.” All the material examined
by the writers from this locality shows a decidedly different color
for the distal half of the large stamen. It seems hardly probable that
material growing in Iowa should show such a marked difference, but in
case this statement is not the result of an oversight on the part of
Professor Todd, it is of considerable interest. The anthers dehisce by
terminal pores, as is common in the genus to which the plant belongs.
The two lower lobes of the corolla are produced into short wings, which
in the bud enfold the pistil and the large stamen, which is clearly
differentiated as such in the youngest buds in which the stamens may be
discerned by careful dissection. In the bud the pistil lies immediately
above the large stamen, but upon the opening of the flower extends
between the filaments of the large stamen and that of the small stamen
either to the right or to the left.
Professor Todd’s statement is: “The pistil in any flower turns toward
the axis of the raceme.” While in a general way this is true, the
statement might be more clearly expressed, since it is only in the
general direction of the pistil as a whole that it points toward the
axis of the raceme.
The style is not inserted perfectly perpendicularly upon the top of
the ovary, but bends slightly downward from the longitudinal axis of
the flower. Professor Todd has overlooked this point in his figure.
Throughout the remainder of its course until near the tip it is almost
straight. Thus it will be seen that the large stamen and the pistil are
placed almost opposite each other on the lower side of the flower. The
angle between their incurved ends, which approach within about three
mm. of each other, is about seventy degrees, thus causing them to point
toward opposite sides of the flower. Thus it will be seen that, since
the flowers are arranged alternately on the opposite sides of a simple,
bractless raceme, and the tip of the large stamen always points toward
the axis of this raceme, the flowers on the opposite sides of the
raceme have both the stigma and the pores of the large stamen turned in
opposite directions.
Professor Todd says: “The flowers are arranged on simple, bractless
racemes which extend in a horizontal position.” The material examined
by the writers does not quite agree with this observation, the most
of the racemes extending upward at a considerable angle. Ten racemes
from different plants were selected at random and their angle above the
horizontal taken. From the table, it will be noted that the nearest
approach to the horizontal is fifteen degrees above, one raceme is
vertical, and the average of the ten is fifty-seven degrees above the
horizontal.