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.