FOOTNOTES:

[A] Harris, J. Arthur: Annotated catalogue of the crayfishes of Kansas. Kans. Univ. Quart., vol. IX, No. 4, October, 1900.

[B] I am not sure, in a trip across country, which of the two creeks, which flow together in this vicinity, I examined.

[C] The water here is probably not more than fifteen degrees above that in which C. virilis was found to be so numb as to be almost incapable of movement. See Harris, Annotated Catalogue.

OBSERVATIONS ON THE POLLINATION
Of Solanum rostratum Dunal and Cassia chamæcrista L.

BY J. ARTHUR HARRIS AND OSCAR M. KUCHS.

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.

  TABLE A.
I 65°
II 75°
III 45°
IV 90°
V 15°
VI 45°
VII 60°
VIII 80°
IX 50°
X 45°
Average   57° 

The terminal portion of the raceme, bearing the buds, is strongly decurved, so that unopened buds obstruct in no way a clear view of the conspicuous flowers, which thus appear to be terminal. The racemes, when in flower, are so far to the outside that the flowers are very little screened by the foliage, whose dark green background renders them more conspicuous.

The fact that the racemes extend upward at some angle from the horizontal, by bringing the flowers above the foliage, renders them more conspicuous.

The terminology used throughout this paper is the same as that suggested by Professor Todd. Those flowers in which the pistil as a whole extends towards the right hand, facing in the same direction as the flower, will be called right-handed, and those in which the pistil as a whole extends toward the left, left-handed. It will be seen that, since the tips of pistil and large stamen approach each other, as above described, the tip of the pistil in a right-handed flower turns considerably toward the left, and vice versa. The flowers on the right-hand side of the raceme, as we pass out from the central axis of the plant, are always left-handed, and those on the left side, right-handed.

Professor Todd found from the examination of a small series of material that about an equal number of right-and left-handed flowers is produced. He also says: “It is also a fact of observation that the flowers of a cluster on any one branch and opening about the same time are either all right-handed or all left-handed. Any plant, however, if it is at all large, exhibits right-and left-handed flowers in about equal numbers.”

The regularity with which the flowers are divided into the two classes is very striking. Table B shows the condition of ten plants observed at the same time.

TABLE B.
Plant I7 pistils right-handed,7 left-handed.
" II6 "    "  6 " 
" III8 "    "  9 " 
" IV29 "    "  31 " 
" V11 "    "  7 " 
" VI  10 "    "  7 " 
" VII10 "    "  13 " 
" VIII3 "    "  3 " 
" IX3 "    "  2 " 
" X6 "    "  9 " 
Total 10 93 pistils right-handed, 94 left-handed.

So in these ten plants the number of right-and left-handed flowers is practically equal. The greatest difference in the number of the two kinds is seen in number X, where forty per cent. are right-handed and sixty per cent. left-handed.

Considerable care was exercised in determining the number of right-and left-handed flowers opening on the racemes of different branches at the same time.

Only those flowers were considered which had opened simultaneously. In order to effect this, all the flowers were removed from the plant the evening before and note was made of the condition of those opening the next day.

The following diagram shows the conditions of flowers opening on three plants on the morning of August 20, braces indicating the branches of the plant, and the straight lines the racemes; the numbers of right- and left-handed flowers being indicated under the raceme by r and l. ([See page 20].)

From the table, it will be seen that there are on the first plant 8 left-and 11 right-handed flowers; on the second, 24 left-and 27 right-handed; on the third, 7 left-and 9 right-handed flowers. The numbers of right-and left-handed flowers occurring on the divisions a and b of the main branches, A and B, of the three plants, are as follows:

On the three plants, with 36 racemes bearing branches, there were 18 branches which produced only one kind of flowers. Of these branches, however, 15 bore only 1 flower each. From this it will be seen that the flowers opening at the same time on any one branch are not all either right-or left-handed. In the large branches, A and B, the number of the two kinds is quite evenly distributed; in only one case-branch B of plant III—is a large per cent. of the flowers alike. Even in branches of the second denomination—Aa, Bb—flowers of one kind occur exclusively, where more than one flower is found, only in Ba of plant III.

In addition to the above table, observations were made on three plants to determine the regularity with which they bore right-and left-handed flowers. On three successive mornings the plants had produced:

I.II.III.
Right. Left.Right. Left.Right. Left.
First morning 7 7 6 6 8 9
Second morning    7 1110 714 17
Third morning16 10 8 1213 10
  Total30 2824 2535 36

It will be noticed that when a marked excess of flowers of one kind occurs one morning, a somewhat proportionate excess of the other type occurs the following morning. This is of course necessary if an equal number of the two types of flowers are to be produced and, to a certain extent, to be maintained on the same plant; and is to be expected from the alternate occurrence of the two types on opposite sides of the raceme.

The flowers open early in the morning and remain open from three to four days, depending somewhat upon the condition of the weather. Some which were covered with cheese-cloth “tents” were noticed to remain open almost a week. At the end of this period the corolla wilts and falls off, as does also the pistil. The flowers seem to partially close at night.

A limited series of experiments were made to determine if self-fertilization and cross-fertilization between flowers of the opposite type opening simultaneously on the same raceme are possible.[I]

The writers have not made sufficiently extensive observations to arrive at any general conclusions of value as to the comparative fertility of cross-and self-pollination, either between flowers on the same or different racemes, or between the flowers of different plants, but they have been able to obtain a limited series of definite results which may be of interest.

In making experiments to determine these points, all old flowers were removed from the plants in the afternoon or evening and the plants covered with a small “tent” of cheese-cloth. The cheese-cloth was of a mesh sufficiently small to prevent the access of any insects large enough to effect pollination, while large enough to allow a ready circulation of air and good illumination. The following morning pollination was effected between the flowers which had opened by tapping pollen from the large anther onto a clean glass slip and transferring it to the stigma of the same or another flower. The plant was then again covered and allowed to remain so, except when examined from time to time, until the corolla and pistil had fallen off. The following results were obtained from three plants upon which observations were made: