June i6, 1893. J 



SCIENCE. 



331 



NOTES ON THE POLLINATION OF PLUMS. 



BY L. H. PAMMEL, AMES, IOWA. 



Some years ago while making a few random examinations of the 

 cultivated DeSoto Plum (Prunus Americana, Marshall) I found 

 to my surprise that the flowers were not all perfect, although 

 described as such. Many flowers have since been examined 

 and I have never failed, in some individuals at least, to find this 

 character well pronounced. 



In all cases examined the suppression was in the direction of 

 the pistil. The stamens in all cases were well developed. In 

 these imperfect flowers the pistil is short, scarcely as long as the 

 calyx tube. In the Rollingstone the pistil is entirely absent in 

 many cases. 



To see how generally the pistils were rudimentary, a number of 

 counts were made on branches selected at random on several 

 trees. 



First Tree. 



These imperfect flowers also occur in the Pottawattamie, but 

 not so commonly as the Rollingstone and DeSoto. I thought at 

 first that these iui perfect flowers might bedue to the improvement 

 of the variety under cultivation, but on examining some seed- 

 lings along an old fence I found that imperfect flowers also oc- 

 curred. Of the enormous number of perfect flowers produced 

 on a single tree a small percentage only develop into plums. 

 They are undoubtedly in many cases fertilized but for want of 

 nutrition fail to mature. 



The flowers of Prunus Americana, in absence of cross pollina- 

 tion, are undoubtedly close pollinated. To test the matter of 

 close fertilization, about 150 flowers were covered with paper 

 bags. Of these fifty set. Between twenty-five and thirty flowers 

 were castrated and pollen applied from other flowers of the same 

 plant with the result that one third set. Considering the circum- 

 stances under which they were made it is a fairly good showing. 



I was much interested this spring to notice that some forms of 

 Prunus domesiiea (Moldavka Plum) are proterogynous. The 

 pistil in some cases protrudes while the flowers are still more or 

 less closed. In other forms of Prunus domestica grown on the 

 college grounds the pistil matures simultaneously with the 

 stamens. This latter condition agrees with Hermann Miiller's ' 

 observations, who says of Prunus domestica, P. avium and P. 

 cerasus, "anthers and stigmas ripen simultaneously and spread 

 apart out of the flower." Prunus padus, L, and P. spinosa, L, 

 according to the same authority, are proterogynous. 



The ijosacece constitute an interesting order of plants, although 

 many of them show adaptations for cross-pollination, they may, 

 at the same time, in absence of cross-pollination, be self- pollin- 

 ated, not, however, in all cases. Strawberry growers are only 

 too familiar with the failure that results when only one variety is 

 set out. 



This tendency to separation of sexes is well marked in widely 

 separated orders and has been admirably discussed by Darwin,'' 

 who says: "There is much difficulty in understanding why 

 hermaphrodite plants should ever have been rendered dioecious." 

 " We can, however, see that if a species were subjected to un- 



' "Fertilization of Flowers," English translation, p. 321. 

 2 "The DltEerent Forms of Flowers on Plants of the Same Species," p. 278, 

 D. Appleton & Co., New York. 



favorable conditions from severe competition with other plants, 

 or from any other cause, the production of the male and female 

 elements and the maturation of the ovules by the same indi- 

 vidual might prove too great a strain on its powers, and the sepa- 

 ration of the sexes would then be highly beneficial." As stated 

 in a previous paragraph, many plum flowers are staminate in 

 function as the fruit never develops. This being the case, it 

 would seem an advantage for the pistil to become abortive and 

 in some cases entirely suppressed. May it not be a step in a 

 direction to prevent self-fertilization, which seems to occur quite 

 commonly in some members of this order, oris it the direct action 

 of climate as Darwin thought to be the case in the strawberry? 



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The editor will be glad to publish any queries consonant with the character 

 of the journal. 



Total Heat Received by a Planet. 



It may be as well to call attention to the shortest method of treat- 

 ing what seems to be the principal point at issue in the articles on 

 "Sun-Heat and Orbital Eccentricity" and on "The Mean Dis- 

 tance of the Earth " in recent issues of Science. 



We have simply for the amount of heat, dh, received by any 

 planet in our system by radiation from the sun, in the infinitesi- 

 mal time (M, on a definite area, say a square foot, of its vertically 

 exposed surface, 



dh = - dt, 

 r- 



in which c is a constant depending on the absolute radiation of 

 the sun, which we suppose to be always the same. 

 But we have 



de 



dtzrz 



k Vp 



in which dt is expressed in terms of the day, d 6 in the usual way, 

 so that 180° = 7r; fc being the Gaussian constant, depending on 

 the mass or absolute attractive force of the sun, and p, the semi- 

 parameter, = a (1 — e^). 



Strictly, we must understand by fc the Gaussian constant 

 0,017203 -f multiplied by V \.-\- u., in which 

 _ mass of planet 



mass of sun 



We have then 



dh: 



-de, 



k Vp 



and for the total heat received by radiation on the definite area 

 in one revolution, 



2 cir 1 

 k ' V~^' 

 Now the major axis being supposed constant, / p" is propor- 

 tional to the minor axis. If then the eccentricity varies in a 

 planetary orbit, the major axis remaining conttant, the quantity 

 of heat received by the planet in one revolution by radiation from 

 the sun is inversely as the minor axis, if the size and mass of the 

 planet and the mass and absolute radiation of the sun remain 

 unchanged. Rev. Geo. M. Searle. 



Catholic University, Washington, D.C. 



A Peculiar Occurrence of Beeswax. 

 Among the heterogenous collections of materials that are con- 

 tinually arriving at the National Museum for the purpose of iden- 

 tification, there were received some weeks ago, from Portland, 

 Oregon, samples of a material closely resembling, if not identical 

 with beeswax. Such it would have unhesitatingly been pro- 

 nounced but for certain stated conditions relating to its mode of 

 occurrence. 



